diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index c92bfe44b8f..87ad89716a4 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -309,15 +309,20 @@ void *chainparams_commandline(void *ptr)
                     (20000, uint256S("0xb0e8cb9f77aaa7ff5bd90d6c08d06f4c4bf03e00c2b8a35a042e760845590c8a"))
                     (30000, uint256S("0xf2112ca577338ad7104bf905fa6a63d36b17a86f914c97b73cd31d43fcd7557c"))
                     (40000, uint256S("0x00000000008f83378dab727864b763ce91a4ea5f75d55939c0c1390cfb8c38f1"))
-                    (49170, uint256S("0x2add646c0089871ec2379f02f7cd60b3af6efd9c152a6f16fc10925458c270cc")),
-                    (int64_t)1529910234,    // * UNIX timestamp of last checkpoint block
-                    (int64_t)63661,         // * total number of transactions between genesis and last checkpoint
+                    (49170, uint256S("0x2add646c0089871ec2379f02f7cd60b3af6efd9c152a6f16fc10925458c270cc"))
+                    (800200, uint256S("0xfa2d5e5f5fb42af9d6343fa93bbc776761341fd754a7e078004132bcd8403dd2"))
+                    (1053660, uint256S("0x0000000000182c0fcba3ae9360417848dd03a8e0cb153f1ee8b4b8f72376de2b"))
+                    (1796400, uint256S("0xeead7e4b5236de7c9fd782d28efa0a288d9188fd40ba7ca9804983035435caec"))
+                    (2549420, uint256S("0x000000000000e1d2915791640dcee0bf36141cc58d436e158fcf126e529083a3"))
+                    (2802250, uint256S("0x000000000002a5c44fd73dab43b2e0cac0dd2b5be6a22d03df5283ca8ee1f8bc")),
+                    (int64_t)1700525524,    // * UNIX timestamp of last checkpoint block
+                    (int64_t)6318742,         // * total number of transactions between genesis and last checkpoint
                                             //   (the tx=... number in the SetBestChain debug.log lines)
-                    (double)2777            // * estimated number of transactions per day after checkpoint
+                    (double)1298            // * estimated number of transactions per day after checkpoint
                                             //   total number of tx / (checkpoint block height / (24 * 24))
                 };
 
-            mainParams.consensus.nMinimumChainWork = uint256S("0x000000000000000000000000000000000000000000000001a8f4f23f8b2d1f7e");
+            mainParams.consensus.nMinimumChainWork = uint256S("0x00000000000d798fd9fc9c92867f40a7000000026e5624a2f47b71ea49cda473");
         }
         else
         {
diff --git a/src/checkpoints.cpp b/src/checkpoints.cpp
index 75597436646..5ba83acd5f3 100644
--- a/src/checkpoints.cpp
+++ b/src/checkpoints.cpp
@@ -59,7 +59,7 @@ namespace Checkpoints {
             fWorkAfter = nExpensiveAfter*fSigcheckVerificationFactor;
         }
 
-        return fWorkBefore / (fWorkBefore + fWorkAfter);
+        return std::min(fWorkBefore / (fWorkBefore + fWorkAfter), 1.0);
     }
 
     int GetTotalBlocksEstimate(const CChainParams::CCheckpointData& data)
diff --git a/src/main.cpp b/src/main.cpp
index ff004e80e7d..f6aa5f20670 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -7728,6 +7728,14 @@ bool RewindBlockIndex(const CChainParams& chainparams, bool& clearWitnessCaches)
 
     PruneBlockIndexCandidates();
 
+    // Ensure that pindexBestHeader points to the block index entry with the most work;
+    // setBlockIndexCandidates entries are sorted by work, highest at the end.
+    {
+        std::set<CBlockIndex*, CBlockIndexWorkComparator>::reverse_iterator it = setBlockIndexCandidates.rbegin();
+        assert(it != setBlockIndexCandidates.rend());
+        pindexBestHeader = *it;
+    }
+
     CheckBlockIndex(chainparams.GetConsensus());
 
     if (!FlushStateToDisk(state, FLUSH_STATE_ALWAYS)) {
@@ -8821,9 +8829,6 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             bool fAlreadyHave = AlreadyHave(inv);
             LogPrint("net", "got inv: %s  %s peer=%d\n", inv.ToString(), fAlreadyHave ? "have" : "new", pfrom->id);
 
-            if (!fAlreadyHave && !fImporting && !fReindex && inv.type != MSG_BLOCK)
-                pfrom->AskFor(inv);
-
             if (inv.type == MSG_BLOCK) {
                 UpdateBlockAvailability(pfrom->GetId(), inv.hash);
                 if (!fAlreadyHave && !fImporting && !fReindex && !mapBlocksInFlight.count(inv.hash)) {
@@ -8990,7 +8995,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "tx")
+    else if (strCommand == "tx" && !IsInitialBlockDownload(chainparams))
     {
         // Stop processing the transaction early if
         // We are in blocks only mode and peer is either not whitelisted or whitelistrelay is off
@@ -9194,6 +9199,18 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             return true;
         }
 
+        // If we already know the last header in the message, then it contains
+        // no new information for us.  In this case, we do not request
+        // more headers later.  This prevents multiple chains of redundant
+        // getheader requests from running in parallel if triggered by incoming
+        // blocks while the node is still in initial headers sync.
+        //
+        // (Allow disabling optimization in case there are unexpected problems.)
+        bool hasNewHeaders = true;
+        if (GetBoolArg("-optimize-getheaders", true) && IsInitialBlockDownload(chainparams)) {
+            hasNewHeaders = (mapBlockIndex.count(headers.back().GetHash()) == 0);
+        }
+
         CBlockIndex *pindexLast = NULL;
         BOOST_FOREACH(const CBlockHeader& header, headers) {
             /*
@@ -9265,7 +9282,12 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         if (pindexLast)
             UpdateBlockAvailability(pfrom->GetId(), pindexLast->GetBlockHash());
 
-        if (nCount == MAX_HEADERS_RESULTS && pindexLast) {
+        // Temporary, until we're sure the optimization works
+        if (nCount == MAX_HEADERS_RESULTS && pindexLast && !hasNewHeaders) {
+            LogPrint("net", "NO more getheaders (%d) to send to peer=%d (startheight:%d)\n", pindexLast->GetHeight(), pfrom->id, pfrom->nStartingHeight);
+        }
+
+        if (nCount == MAX_HEADERS_RESULTS && pindexLast && hasNewHeaders) {
             // Headers message had its maximum size; the peer may have more headers.
             // TODO: optimize: if pindexLast is an ancestor of chainActive.Tip or pindexBestHeader, continue
             // from there instead.
@@ -9540,7 +9562,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         // message would be undesirable as we transmit it ourselves.
     }
 
-    else {
+    else if (!(strCommand == "tx" || strCommand == "block" || strCommand == "headers" || strCommand == "alert")) {
         // Ignore unknown commands for extensibility
         LogPrint("net", "Unknown command \"%s\" from peer=%d\n", SanitizeString(strCommand), pfrom->id);
     }