2500k all the way. There is no possible way that 2mb L3 cache and Hyperthreading are worth the extra $100 for the 2600k. And at a stock frequency of 3.3Ghz, even if you don't overclock it will still be a very strong CPU. However, with the possibility of hitting upwards of 4.6-5.0Ghz with the right board and cooling solution, I would say Overclocking is the thing to do.
As for the choice of motherboard, it might be smart to wait and see what the other manufacturers come out with. It should be anytime now before all the rest of them release their own revised versions for the P67 chipset. My 2 cents...
