AMD Athlon 64 3000+ OC'ed to 2.52 GHz Stable at 11+ hours on Prime95. Have taken it up to 2.74 GHz but failed Prime95 after ~ 30 minutes with .5/.4 rounding error ... but was able to do 3DMark2005 on it and get a rating of 8897 with an eVGA 7800GTX and was also able to play BF2 for a while ... didn't crash on me ... but wouldn't last on Prime95. HSF combo is XP-90 w/ ThermalTake SilentCat 90mm fan.
Images below are for 11+ hour stable on Prime95 with AMD Athlon 64 3000+ OC'ed to 2.52 GHz and RAM at 422 (210) MHz.
CPU (2600+ XP-Mobile) runs on 1.7V
Ram is PC3200 Mushkin Level II Black 2-2-2 (TCCD)
Currently air cooled, ThermalRight SP-97 + Panaflo High. Load temps on a hot day often reach 55 Celcius. Idle usually hovers around 43-44 Celcius.
I have some more headroom, but I'm waiting for my watercooled case to be ready before going higher.
http://valid.x86-secret.com/show_oc?id=36893
I managed to get it to about 2.37GHz, but it was unstable. 2.38GHz and my system rebooted. I didn't touch the voltage though. It's running at the stock voltage which is 1.392v.