I had a 2.6c p4 h/t and i overclocked it to 3.2ghz on stock heating. I overclocked my 6800 100mhz higher on memory and gpu. And unlocked the pipelines. I LOVE IT!
I got my 2500+ permanantly overclocked to 3200 speeds (can't remember clock rate) on DDR500 memory with uber-low timings. Thing is, i need to get better cooling, since its running on stock. My case manages to keep it quite cool though, currently running at 43C (i got a temp probe on the underside of the ACTUAL CPU linked up to an LCD on the front of the case). Thinking about getting water cooling once i get another harddrive, more RAM and a new mouse+keyboard.
As for my Radeon, i got it clocked at stock speeds since i don't game all that much. Well actually i do now, but I cant be bothered to find good clocks.