It depends on the game. If it's SC2 or the original Crysis, then you'll be bottlenecked with that setup in some situations if you're talking about the vanilla 2600 and not the 2600k. Must overclock 2500/2600k to 4.5 to push a min of 60 FPS in SC2 and ~4.8 in Crysis1. I don't know of any other games for which it would be a problem.
I thought the 2600 had a stock of 3.4, is it really possible to safely OC all the way up to 4.8 (even if you spend a bunch on ridiculous cooling systems)?
But, most games (save SC2, Crysis and apparently Skyrim) I play will have the same FPS whether my core is at 3.4Ghz or 4.0+?