So far there was no game that i couldn't play at the highest settings, i tried games like crysis, gta4 and bc2.
Only Metro 2033 gets slowdowns on highest settings, though that game seems to lack some serious optimizing.
(Its still running at a smooth framerate, but on "high" setttings, which pretty much looks as good as "highest", its a lot more enjoyable since it runs at a constant 60+ fps.)