Analyzing Gnutella traffic more... I especially like idea 4: grouping Queries or Queryhit together and so avoid protocol overhead and also use routing tables (server inside) and TCP/IP more efficient.

While I really like this idea... wouldn't it break v0.4 backwards compatibility? Or do you think we don't care because v0.4 clients will be soon outdated and rare to find. A possible solution could be, when you're connected to a v0.6 client group Queries/Queryhits together where possible, if you're connected to a v0.4 client split them up into single messages again.