Yesterday I have purchased Far Cry 2 from the steam store due to the low price and hearing recommendations regarding the game.
Last night I played for about 2 hours or so on Very High settings with 2x AA. (With fps steady above 45 at all times)
Tonight I got into the game with the same settings and I was getting about 15 Fps, so I lowered AA to None, and then I was getting 17-22 Fps.
Very strange Ubisoft...
Here is the first try to fix the problem. It is called "Verify Integrity Of Game Cache". Do this a few times in a row to make sure all the files are down loaded it only takes a few minutes each time. Good luck.
TOOL: When in Steam, left click on Games. Then left click on view Games Library. Right click on the Game. Then left click on properties. Then left click on local files. Then left click on Verify Integrity of Game Cache.