fix update of best chunk size

src/shred.cpp

@@ -136,6 +136,22 @@ void Shred::evaluateThroughput(Drive *drive)
                                         " MB/s with " + to_string(currentChunkSize / (1024 * 1024)) +
                                         " MB chunks - Drive: " + drive->getSerial());
             }
+            else if (currentChunkSize == bestChunkSize)
+            {
+                // Update best throughput when measuring at best chunk size
+                // This ensures bestThroughputMBps reflects CURRENT performance, not old burst
+                if (throughputMBps < bestThroughputMBps)
+                {
+                    Logger::logThis()->info("Updating best throughput: " +
+                                            to_string((int)bestThroughputMBps) + " MB/s -> " +
+                                            to_string((int)throughputMBps) + " MB/s " +
+                                            "(sustained performance at best chunk size: " +
+                                            to_string(bestChunkSize / (1024 * 1024)) + " MB)" +
+                                            " - Drive: " + drive->getSerial());
+                    bestThroughputMBps = throughputMBps;
+                }
+                throughputIncreasing = false;
+            }
             else
             {
                 throughputIncreasing = false;