diff --git a/etc/controlDict b/etc/controlDict
index ea88edf7d7..f6940660f0 100644
--- a/etc/controlDict
+++ b/etc/controlDict
@@ -130,7 +130,9 @@ OptimisationSwitches
     // Number processors to change to tree communication
     nProcsSimpleSum 0;
     // Min numProc to use non-blocking exchange algorithm (Hoeffler: NBX)
-    nonBlockingExchange 0;
+    nonBlockingExchange 1;
+    // Use hybrid NBX/PEX for PstreamBuffers
+    pbufs.algorithm 0;
 
     // MPI buffer size (bytes)
     // Can override with the MPI_BUFFER_SIZE env variable.
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.C b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.C
index c8de9f243e..547b77c8d1 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.C
@@ -27,7 +27,6 @@ License
 \*---------------------------------------------------------------------------*/
 
 #include "PstreamBuffers.H"
-#include "bitSet.H"
 #include "debug.H"
 #include "registerSwitch.H"
 
@@ -36,7 +35,7 @@ License
 int Foam::PstreamBuffers::algorithm
 (
     // Not really the most creative name...
-    Foam::debug::optimisationSwitch("pbufs.algorithm", -1)
+    Foam::debug::optimisationSwitch("pbufs.algorithm", 0)
 );
 registerOptSwitch
 (
@@ -134,8 +133,7 @@ void Foam::PstreamBuffers::finalExchange
 
 void Foam::PstreamBuffers::finalExchange
 (
-    const labelUList& sendProcs,
-    const labelUList& recvProcs,
+    const labelUList& neighProcs,
     const bool wait,
     labelList& recvSizes
 )
@@ -155,7 +153,7 @@ void Foam::PstreamBuffers::finalExchange
             // Preserve self-send, even if not described by neighbourhood
             recvSizes[UPstream::myProcNo(comm_)] = 1;
 
-            for (const label proci : sendProcs)
+            for (const label proci : neighProcs)
             {
                 recvSizes[proci] = 1;  // Connected
             }
@@ -172,8 +170,7 @@ void Foam::PstreamBuffers::finalExchange
         // PEX stage 1: exchange sizes (limited neighbourhood)
         Pstream::exchangeSizes
         (
-            sendProcs,
-            recvProcs,
+            neighProcs,
             sendBuffers_,
             recvSizes,
             tag_,
@@ -626,7 +623,7 @@ void Foam::PstreamBuffers::finishedNeighbourSends
     const bool wait
 )
 {
-    finalExchange(neighProcs, neighProcs, wait, recvSizes);
+    finalExchange(neighProcs, wait, recvSizes);
 }
 
 
@@ -637,71 +634,7 @@ void Foam::PstreamBuffers::finishedNeighbourSends
 )
 {
     labelList recvSizes;
-    finalExchange(neighProcs, neighProcs, wait, recvSizes);
-}
-
-
-bool Foam::PstreamBuffers::finishedSends
-(
-    bitSet& sendConnections,
-    DynamicList<label>& sendProcs,
-    DynamicList<label>& recvProcs,
-    const bool wait
-)
-{
-    bool changed = (sendConnections.size() != nProcs());
-
-    if (changed)
-    {
-        sendConnections.resize(nProcs());
-    }
-
-    // Update send connections
-    forAll(sendBuffers_, proci)
-    {
-        if (sendConnections.set(proci, !sendBuffers_[proci].empty()))
-        {
-            // The state changed
-            changed = true;
-        }
-    }
-
-    UPstream::reduceOr(changed, comm_);
-
-    if (changed)
-    {
-        // Update send/recv topology
-        labelList recvSizes;
-        finishedSends(recvSizes, wait);  // eg, using all-to-all
-
-        // The send ranks
-        sendProcs.clear();
-        forAll(sendBuffers_, proci)
-        {
-            if (!sendBuffers_[proci].empty())
-            {
-                sendProcs.push_back(proci);
-            }
-        }
-
-        // The recv ranks
-        recvProcs.clear();
-        forAll(recvSizes, proci)
-        {
-            if (recvSizes[proci] > 0)
-            {
-                recvProcs.push_back(proci);
-            }
-        }
-    }
-    else
-    {
-        // Use existing send/recv ranks
-        labelList recvSizes;
-        finalExchange(sendProcs, recvProcs, wait, recvSizes);
-    }
-
-    return changed;
+    finalExchange(neighProcs, wait, recvSizes);
 }
 
 
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.H b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.H
index 68a3c81d32..ad811fc784 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamBuffers.H
@@ -108,9 +108,6 @@ SourceFiles
 namespace Foam
 {
 
-// Forward Declarations
-class bitSet;
-
 /*---------------------------------------------------------------------------*\
                        Class PstreamBuffers Declaration
 \*---------------------------------------------------------------------------*/
@@ -168,8 +165,7 @@ class PstreamBuffers
         //  (nonBlocking comms).
         void finalExchange
         (
-            const labelUList& sendProcs,
-            const labelUList& recvProcs,
+            const labelUList& neighProcs,
             const bool wait,
             labelList& recvSizes
         );
@@ -435,25 +431,6 @@ public:
             const bool wait = true
         );
 
-        //- A caching version that uses a limited send/recv connectivity.
-        //
-        //  Non-blocking mode: populates receive buffers.
-        //  \param sendConnections on/off for sending ranks
-        //  \param sendProcs ranks used for sends
-        //  \param recvProcs ranks used for recvs
-        //  \param wait wait for requests to complete (in nonBlocking mode)
-        //
-        //  \return True if the send/recv connectivity changed
-        //
-        //  \warning currently only valid for nonBlocking comms.
-        bool finishedSends
-        (
-            bitSet& sendConnections,
-            DynamicList<label>& sendProcs,
-            DynamicList<label>& recvProcs,
-            const bool wait = true
-        );
-
 
     // Gather/scatter modes
 
diff --git a/src/finiteVolume/fvMesh/zoneDistribute/zoneDistribute.C b/src/finiteVolume/fvMesh/zoneDistribute/zoneDistribute.C
index aae092a6d0..806ce43d0d 100644
--- a/src/finiteVolume/fvMesh/zoneDistribute/zoneDistribute.C
+++ b/src/finiteVolume/fvMesh/zoneDistribute/zoneDistribute.C
@@ -109,9 +109,7 @@ void Foam::zoneDistribute::setUpCommforZone
             }
         }
 
-        // Stream the send data into PstreamBuffers,
-        // which we also use to track the current topology.
-
+        // Stream the send data into PstreamBuffers
         pBufs_.clear();
 
         for (const int proci : pBufs_.allProcs())
@@ -126,7 +124,7 @@ void Foam::zoneDistribute::setUpCommforZone
             }
         }
 
-        pBufs_.finishedSends(sendConnections_, sendProcs_, recvProcs_);
+        pBufs_.finishedSends();
 
         for (const int proci : pBufs_.allProcs())
         {
diff --git a/src/finiteVolume/fvMesh/zoneDistribute/zoneDistribute.H b/src/finiteVolume/fvMesh/zoneDistribute/zoneDistribute.H
index 3b0e182a58..87fb283aa4 100644
--- a/src/finiteVolume/fvMesh/zoneDistribute/zoneDistribute.H
+++ b/src/finiteVolume/fvMesh/zoneDistribute/zoneDistribute.H
@@ -93,15 +93,6 @@ class zoneDistribute
         //- Global cell/face index to send for processor-to-processor comms
         List<labelList> send_;
 
-        //- Parallel [cache]: send connectivity (true/false)
-        bitSet sendConnections_;
-
-        //- Parallel [cache]: send data to these ranks
-        DynamicList<label> sendProcs_;
-
-        //- Parallel [cache]: recv data from these ranks
-        DynamicList<label> recvProcs_;
-
         //- Persistent set of exchange buffers
         PstreamBuffers pBufs_;
 
diff --git a/src/finiteVolume/fvMesh/zoneDistribute/zoneDistributeI.H b/src/finiteVolume/fvMesh/zoneDistribute/zoneDistributeI.H
index 9be368d10f..b45528d5f5 100644
--- a/src/finiteVolume/fvMesh/zoneDistribute/zoneDistributeI.H
+++ b/src/finiteVolume/fvMesh/zoneDistribute/zoneDistributeI.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2019-2020 DLR
-    Copyright (C) 2020-2022 OpenCFD Ltd.
+    Copyright (C) 2020-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -161,18 +161,6 @@ Foam::Map<Type> Foam::zoneDistribute::getDatafromOtherProc
 
     if (UPstream::parRun())
     {
-        if (sendConnections_.empty())
-        {
-            WarningInFunction
-                << "The send/recv connections not initialized - "
-                << "likely that setUpCommforZone() was not called"
-                << endl;
-            // But don't exit/abort for now
-        }
-
-        // Stream the send data into PstreamBuffers,
-        // which we also use to track the current topology.
-
         pBufs_.clear();
 
         for (const int proci : pBufs_.allProcs())
@@ -198,7 +186,7 @@ Foam::Map<Type> Foam::zoneDistribute::getDatafromOtherProc
             }
         }
 
-        pBufs_.finishedSends(sendConnections_, sendProcs_, recvProcs_);
+        pBufs_.finishedSends();
 
         for (const int proci : pBufs_.allProcs())
         {