Assassin's Creed II performance issues

I am playing it on a 5870, and the game is fully patched and I am using the latest drivers. I have a Phenom II x4 965 and 8gb ram. I am getting performance from 30-63 fps, and sometimes the game dips below 30. I am playing it with maxed out settings with 4xaa. Any suggestions to improve the performance of this game?

There's not much that you can do I'm afraid. The assassin creed games don't run perfectly on my pc either and I have a gtx 580.

I managed to get brotherhood to stop stuttering but those fixes don't work on assassins creed 2.

If you do manage to work it out, please post your fixes.

That's odd. Surely it's a problem with newer cards, since I can run it maxed out on my 9800GTX+ with no performance problems at all.