Short: AMD Athlon 64 X2 5000+ BE 2,6GHz @ 3,2GHz. Long: I bought Phenom 9600 BE 2,3 GHz, but it got cooked the next day, while waiting, I bought Athlon, which is so much faster and cooler, so i ditched Phenom.
With that processor on my old system I never could overclocked it higher than 3,0. 3,2 is a good overclock. Which motherboard do you've?
ASUS M3A32-MVP Deluxe, CPU is cooled by Thermalright Ultra 120 Extreme + NF-P12-1300 (AC MX2 paste) in Lian Li PC-P60 ArmorSuit Black with 5xNF-P12-1300. I had to increase CPU voltage to 1,4V to get over 3 GHz, but I could not get it through 3,3 GHz, no matter what, pity. Idle is 38C in this heat and burn about 60C. I think about Phenom II 955, which can be overlocked to 3,6-7GHz - 3,8GHz dramatically increase power usage, but 5% increase in performance is not worth it.
Kinda of hard poll to do since there is so many PU you could have that still can run OS. Intel and AMD can be OC. In the past more OC today a lot of dual/X2 quad/x4 dual quad/x8(whatever) frankly are okay at the speeds they come stock with. OC hardward tends to fail more if you leave it alone as the rated stock speed. I OC all the PU even C, N, G.
AMD PII X6 1055T @ 3.5GHz (default voltage) cpu core temp @ idle 27C (room temp 25C) @ load under Prime95 torture 43C
Intel Core 2 Duo T7600G 2.33Ghz and over clockable to 3.2GHz. The first unlocked processor for Laptops! http://www.cpu-world.com/CPUs/Core_2/Intel-Core 2 Duo Mobile T7600G LF80537GF0534MU.html TH
Xeon Quad 3350 @ 2.66 ghz. Wouldn't mind trying an overclock but it's seems fast enough as is and I'm not really all that confident or experienced in the overclocking side of things.
Two 2.26GHz Quad-Core Intel Xeon "Nehalem" processors AMD Athlon(tm) 64 X2 Dual Core Processor 4000+ AMD Athlon(tm) XP 2600+ Intel Pentium 4 Intel Pentium II Overclock? No.
Intel Core 2 Duo Processor E7200 (3M Cache, 2.53 GHz, 1066 MHz FSB) No overclocking of processor, but have adjusted RAM timing to optimum settings.
