IIRC at 3.4ghz, you're already pushing the p4 3.4c core, while the 3400+ under the right mobo, MIGHT have better yields
gaming on the athlon will be better, but multimedia the p4 shines, but since you do both, its your call
btw, if you're only getting DDR400 ram, get the athlon64, because the athlon doesnt require 1:1 to really shine - the p4 needs memory bandwidth like a mofo