いじる対象となるパラメータはこのぐらいかしら。
ちなみに値は適当。

・/etc/sysctl.conf
# special setting for HTT, but...
#machdep.cpu_idle_hlt=1
# increase IP port range
net.inet.ip.portrange.last=20000
# enable new feature on TCP for FreeBSD 4.7 or later
net.inet.tcp.inflight_enable=1
# increase maximum file descriptors
kern.maxfiles=65536
kern.maxfilesperproc=32768
# increase listen queue
kern.ipc.somaxconn=4096
kern.ipc.maxsockbuf=1048576
# do not use swap area (it's slow)
vm.defer_swapspace_pageouts=1
vm.disable_swapspace_pageouts=1

・/boot/loader.conf
kern.maxusers=512
kern.ipc.nmbclusters=32768
kern.ipc.maxsockets=32768