depends on the CPU and motherboard, but usually 4GHz is easy on a black edition.
just download coretemp to watch temps and make sure you stay in the 50s or lower, C
not-so-crappy 775 System:
Q8400 @ 3.8GHz 1.37v 24/7 - GA-EP45-UD3R v1.1 F12 - 4GB (2x2) OCZ Reaper HPC DDR2 1066 CL5 2.1v
EVGA GTX460 1GB 815/1950, w/ ACER 23" 1920x1080 TV & Dell UltraSharp 20" 1600x1200In Progress:
ThermalTake Armor A90 chassis function modded, 2x4GB GSKILL RipjawsX DDR3 2133 CL9, Corsair HX-750wRemaining:
Board / CPU / other 2x4GB CL9 ripjaws kit / GPU upgrade