I like to tweak OS's so this is a network performance tweaks I do to Mac OS X 10.7.
Website I found some information.
http://support.apple.com/downloads/Broadband_Tuner_1_0
http://slaptijack.com/system-administration/mac-os-x-tcp-performance-tuning/
Start up a Terminal window and type information below.
$ sudo pico /etc/sysctl.conf and add information below.
net.inet.tcp.rfc1323=1
#kern.ipc.maxsockbuf=16777216 Max size seems to be 6291456 which is the default setting.
net.inet.tcp.sendspace=1048576
net.inet.tcp.recvspace=1048576
Restart workstation for these parameter's to take affect.
Adding this to the sysctl.conf file seems to make my network perform at a more stable rate when testing at Speedtest.net.