The q6600 or the 9450. The 45nm quads were having stability issues though, so they got pushed back. The prices on the q6600 are rediculous right now though, with a good cooler you can run it easily at 3.6ghz. FWIW, to run a 9450 at 3.6ghz, you are going to need a good motherboard that can support 450mhz FSB, since it only has an 8x multi.