Shit, I'm still running on a Kentsfield C2Q 6600 with no problems - an I7 is still pretty top shelf in my opinion.
Stay the hell away from the Bulldozer chips, is what I hear through the grapevine, as far as late breaking CPU news goes.
There's been a big to-do about moving from the 45 to 32 nm chips, but in my opinion you get more bang for your buck out of a GPU upgrade, rather than riding the cutting edge of the CPU trends.