I've been testing FreeBSD 8 at work to determine viability for replacing our current FreeBSD 7.2 server. I encountered similar issues to you
khakkinen in terms of network performance.
Mine are running as guests under VMware ESXi 4 Update 1. My biggest issues has been disk I/O performance, but that seems to be regardless of which version of FreeBSD I'm running. I benchmarked each system using NUTTCP (network) and DD (disk).
My results averaged the following:
FreeBSD 7.2- 900Mbit/s network throughput
- 14MB/s disk transfer speed
FreeBSD 8.0- 500Mbit/s network throughput
- 11MB/s disk transfer speed
My network performance is down by a huge 45% and my already crippled disk performance is down another 20%. I've tried various tweaks (I was going to link you the tweaks I used, but apparently I'm not allowed) to improve performance, but it doesn't seem to make any difference.