I'm weighing the pros and cons between a Lynnfield system, and one centered around the i7 920. The 2.8GHz Lynnfield processor will be faster in games that aren't threaded well, due to its aggressive turbo mode. When 3 or less cores are active, the Lynnfield processor should be faster, and only when that 4th core is needed will the i7 920 end up more effective.
I ponder for a second whether DX11 will change the picture at all. If DX11 uses multi-core CPUs more efficiently, and that 4th core is utilized more, then perhaps the i7s will be the way to go.
Unfortunately, any way I slice it a Phenom II system just won't be good enough compared to a Lynnfield. And since the only reason why Phenom IIs are viable, is because of bad scaling, and poor support for multiple-cores and threads... DX11 could amplify that gap between Intel and AMD processors in new games.
AMD has about to November to release something that doesn't suck, or the shit's going to start hitting that fan hard for them.