It depends on your video card as well. If you don't have at least a 9700Pro/5800U you probably won't see much of a difference
yep, agreed. i have a 9800xt now with an x800 xt ordered (when all is said and done the gpu upgrade will cost me $149.00

).
i o/c my cpu's as high as they can go on stock voltage then back off a tad (since it's voltage that'll kill a P4 and not heat) but i don't want to go out and get a 3.4 if all i'll get out of it is around 3.8ghz. a 400mhz increase isn't worth a $265.00 expenditure ($415.00 - $150.00 for my 2.8= $265.00) to me.
i'm now considering a 3.2. if i can get 3.8 out of a 3.2 than that's more reasonable. i know the rest of my system can handle 250+fsb easily since i've tried it. the upgrade to a 3.2 would cost a $120.00.