Dont fetch ahead if cbopret chain, yes it will slow it down

src/main.h

@@ -111,7 +111,7 @@ static const unsigned int MAX_HEADERS_RESULTS = 160;
  *  Larger windows tolerate larger download speed differences between peer, but increase the potential
  *  degree of disordering of blocks on disk (which make reindexing and in the future perhaps pruning
  *  harder). We'll probably want to make this a per-peer adaptive value at some point. */
-static const unsigned int BLOCK_DOWNLOAD_WINDOW = 1024;
+static unsigned int BLOCK_DOWNLOAD_WINDOW = 1024;
 /** Time to wait (in seconds) between writing blocks/block index to disk. */
 static const unsigned int DATABASE_WRITE_INTERVAL = 60 * 60;
 /** Time to wait (in seconds) between flushing chainstate to disk. */