if you get bad framerates at high, drop down to lowest, if you're getting much higher framerate it means your cpu is more than capable of higher settings. maybe the only differences would be physics to a not top setting might help i'm not sure. try it.
high ran at an acceptable but not perfect framerate on my 2900xt, as people may or may not have noticed, AA is dodgey at best in most recent games. firstly they are doing things in engine to make aa less of an issue in the first place, some of the games flat out don't support AA, and its really not needed anywhere as badly as titles in general from well every title before the latest crop of games. clearly the industry is moving away from normal AA and is doing a lot to do AA within the engine itself. i played without AA and didn't notice much wrong in that sense. sure if you stand still near a sharp edge for half an hour you'll probably notice something. but in actual play, moving around its not that bad. but then i was playin at 1680x1050, might be worse at lower levels.
theres not a huge amount going on with the cpu in general, its most likely, like other games, simply splitting off different parts of the engine to diff cores if available, IE, sound, maybe physics(maybe not), input, drivers, blah blah. but in general its still incredibly difficult to split the main engine into multiple parts. we're still at the point where fps's dont entail a huge amount of cpu power anyway. you don't just use cpu for the sake of its there. what do you think they should add to the game exactly that uses cpu power that would make it better.
its a gpu load game, it looks fantastic, high/very high look easily better than anything around and that takes more power than games that don't look as good.
if you DO have to complain about framerate, don't post a generic sentence, post YOUR SETTINGS. that means res, aa/af, and the settings in game. that way if someone with a similar rig posts and says he's got twice your fps and the only difference is one small setting, you might be able to help yourself. if people just post their actual settings , and compare them we might find some easily changable option that makes the game play great for everyone. but why do that when you can just complain and move on.........
quad core support most certainly is a marketing buzzword, as basically all games with "quad core support" shows. lets see, sup commander, dual core, a modest boost in fps, quad core about 1-2% further on top of that. but the fact is its plenty playable in most situations on a single core, its more than fine on dual core as most people who played it had single/dual and were fine with it.
ut3 still plays pretty well on a single core, perfect on a dual, and theres very VERY little difference at REAL resolutions with a quad core.