I have 8gb of ram, win7 64, and a quad 2.33, and I still get some heavy lag in huge battles. I fiddled with the settings for a long time, and even had to replace my video card because it strangely burned out while playing this game! I found that changing from directX 9 to 7 helped enormously and I was able to crank the settings back up. It seems to have something to do with the shadows being generated I think, as I've had issues with that before on other games. Try giving that a shot and see if it helps some.