if that Q6600 is a G0 revision you can overclock it to 3+ GHz for "free"... apart from that you'd be fine playing in high-ultra as long as you lock the framerate to 30, that CPU can't deliver a smooth 60 fps experience since the dips are too frequent and huge, my brother has the same setup as mine but I upgraded to a 3570K... on the other hand my bro is so stubborn he loves his old Q6600 and say it can still run anything, we both have some 7950 Boost 3 GB, the game runs beautifully in my system , with the loading stuttering of course... but his same system running the Q6600 looks like a roller coaster with the framerate all over the place, time to upgrade that CPU ! for 1080p 30fps locked it's fine though as far as I've seen, that CPU got indeed some legs when overclocked.
It's a pre-built Dell. Can't overclock and can't change the CPU without changing the whole motherboard. I'm stuck with it as-is until I get a whole new system.
It's run almost everything on high settings really well except specific instances. I think I got a lot of frame drops on Dishonored most recently. But I don't use FRAPS or anything to track framerate.
I'll probably just keep it on high. Plus, I usually keep AA down to 2x because I don't really care that much about it beyond 2x.