I don't know man, I just played CS:Source for the first time at a LAN this past saturday, everything cranked maxed, although I don't think I had an AA or AF on...and I didn't notice any slowdown at all....I haven't run the stress test though so I'll get back to you on that
But keep in mind people, anything over 50, hell even 40 FPS is considered smooth. It's lame to see people saying 'What the hell! I only get 80 instead of 90 FPS'
EDIT: Aright, did two video stress tests with source:
All maxed out details of course
215MHz DDR430 RAM with 2.5-3-3-7 timings
incase you guys wanted other specs.
6600GT stock speeds.