I've screwed with this alot because I like playing huge maps against AI and I know it can be a pain in the ass later in game where you see GPU utilization at 20 percent and you are getting 25-30 FPS. All I can say is it's CPU bottlenecking. Make sure your northbridge is working with the RAM not against. On stock clocks i can play a huge multi random game against all ai, then the FPS shat the bed about 4 hours in. (20-25.) Bumping the northbridge from 2000 to 2400, reseting mem timings to 6clk and kicking the cpu up from 3.4g to 4.1g picks up about 100 percent improvement to playable FPS 45-55. It still has one core running at 100 percent but the performance is better. I suppose it you could get a dual core up to stable 4.8g-5.0g you could play most anything at 60+ fps but that's ridiculous.