Even with no AA I would still not expect you to be able to get 40 FPS with that hardware.
I guess maybe I judged the performance of the parts to low.
I don't have the game myself, I just know what I have been reading and it seems to conflict with your results. I guess maybe I am getting low AA confused with no AA.
To be fair about it, most people aim for 60 smooth FPS too, because that is about the sweet spot where you don't notice any lag normally and the worst lagging parts usually still result in a reasonable 40ish FPS.
I would expect that if the best places do 40 FPS then the worst places probably get under 30 and maybe even under 20 which would potentially be unfavorable.
That being said, if you like it how it is that is great.
well i get 50 fps inside of buildings typically and 40 fps outside, and the only time that it drops below 30 is if a massive barrel of oil or something explodes next to me and that brings it down to like 20 for a few seconds, but if im running it pretty well now then ill hold off on upgrading till the generation after ivy bridge....anyways here is the nvidia page with the settings i used and the average fps of it if youre curious