Apple has released
Broadband Tuner v1.0, a utility that tweaks the system parameters of Macs with very high speed Internet connections — 5 Mbps or faster.
Broadband Tuner changes the default values for the size of the TCP send and receive buffers used by Mac OS X, according to Apple. “With larger buffers more data can be in transit at once,” said Apple. “A startup configuration file is also updated so that these changes will persist across restarts.”
An optional uninstaller can be used to restore the system settings that were in effect before the parameters were changed. System requirements call for Mac OS X v10.4 or later.