IBM introduced Streaming Replication with Lotus ND6. If a Lotus Notes Version 6 Client connects to a ND6 server for replication, this new replication process should speed up the replication. If you want to see more detailed information on replication on your server you may want to test some of the new notes.ini debug parameters:
DEBUG_STREAMING=1
DEBUG_STREAMING_REPL=3
DEBUG_BAD_BUFFERS=1

If you want to measure the difference in replication on ND6 you can temporarily disable Streaming Replication by using
DEBUG_ENABLE_STREAMING_REPLICATION=0
in your servers notes.ini. Please note that Streaming Replication is not used for initial replication or replicating after deleting the replication history.