I have two first gen dual 1ghz CPUs. One says 7455a and the other just says 7455. Both are out of first generation MDD machines. The first one I tried 1.33ghz at 1.95v (1.85v is stock) and it wouldn't even attempt to boot, but chimed. Same voltage at 1.25ghz resulted in it almost booting, KP'ing right before the GUI started. The second chip wouldn't even do anything at 1.25ghz at 1.95v. I just dropped it back down to 1.85v and 1.08ghz and it seems to be running stable (several passes of geekbench with 1011 score and CPUTest). I know all chips don't overclock the same, but this seems like terrible luck. Anyone have better success with these chips?