tcp tuning and oprofile

[Mr Y]

Hello,

I'm trying to improve my 10GigE driver performance on FreeBSD 6.3.
till now I found the following tcp parameters and set them:
# sysctl net.inet.tcp.sack.enable=0
# sysctl kern.ipc.maxsockbuf=16777216
is there anything else I should think about regarding tcp parameters?

2nd question:

I'm getting quite a high cpu utilization, about 75% for an iperf test.
I'm looking for a tool such as oprofile that will help me find the problem.
does anybody know something like that?

Thanks,
-Yony