well, i was going as far as i could with a couple of my older computers, and my buddy's and i got some pretty decent clocks.
the difference in performance is night and day.
here is an example, when the P4c's first came out, me and a buddy of mine both got ours
me, 3.0c, stable as a rock a 3.4, then motherboard failure. Abit is-7
got a DFI infinity 875p, clocked great, another 100mhz, and even better performance, but the raid controller sucked, and after a couple weeks, the ethernet adapter went bad. my raid performance was lower than most people's standard IDE. Highpoint btw, not my favorite raid controller.
MSI 865 board, didn't clock well, just didn't work with my setup, so i got an Asus p4p800, didn't clock as well as the DFI, but hasn't given me a lick of problems since i bought it, and the HDD perform like they are supposed to.
my friend, 2.4, MSI 875p, 275fsb for a LONG time, 3.3ghz, very stable, then got some upgraded cooling, went to 300fsb. that's 3.6 ghz, a 50% overclock, for 8 months, no problems, now he has to try to boot his computer twice, everytime.
it actually ran at 3.8ghz for a short period of time on air cooling.
moral of the story, my computer, at stock 3.0 will do anything i ask of it, that's why i stopped overclocking.
if your computer isnt doing what you want, then by all means, overclock a little, but beware, because sometimes, it Does have consequences.