C2D, but no reason to believe the i5/i7 will be any different. Swapping the 2.66 i5 for a 2.93 i7 shouldn't be much of a hassle, if you're not afraid of being on your own warranty!
I wonder if apple changed the thermal layout between the i5 and the i7, if so it'll be more of a hassle andmight not even be feasible to replace the i5 with the i7 down the road.