I'm pushing flash video with lighttpd from a couple servers, and I seem to be running into a sort of speed limit. The servers simply won't push any more than 340-370Mbps.

The thing is, they are not under that much load at that point. Plenty of CPU and RAM free. Files are pulling from a fibre channel SAN (I've also tested with a ramdisk), so disk access speed is not the issue. The NICs are good (e1000, Allied Telesyn AT-2971 with skge driver). I'm also not hitting the max connection limit on the webserver.

I have a Quagga router that can saturate a gigabit card, so why can't these webservers do it?

Servers are running Gentoo 2007.0 with 2.6.22 kernel.

are the NICs and switch both hard set for Full Duplex?

Yes, the NICs are hard set to Full Duplex, speed 1000