What's in the USB upgrade? The biggest bottleneck you've got with a laptop is the graphics. I can't imagine that you're going to get better graphics over USB.

I run AFP on a Celeron 2GHz, 1GB ram and a PCI Radeon 9100. I'm using a 24" Dell flat panel and have the display set to 1920x1200. It works fine and I get 30-90FPS.

Someday when I've got the cash I'll upgrade to AFPD(or its follow on) and get a fast gaming system to run it on, but AFP works for what I need.