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.
Start up a Terminal window and type information below.
$ sudo pico /etc/sysctl.conf and add information below.
#kern.ipc.maxsockbuf=16777216 Max size seems to be 6291456 which is the default setting.
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.