Hey, if you can afford an i7, knock yourself out. All the new Intel stuff will use the new socket, so if you're buying anyway, I would muscle up on the CPU and good mid-range GPU. From what I can see, this sim is heavier on the CPU rather than the GPU. Any current generation video card should be fine. I'm running a 9800GT at 1280x960 and get 40fps. But I only have a Core 2 Duo 6750. When the AI engages me I notice a spike in CPU activity.
Oh yeah, and the i7 920 can be clocked up to 4Ghz with adequate cooling. It'll run faster than the i7 Extreme. If I could afford it, it'd be mine.