The upcoming Phenom X4 processor from AMD won't offer much more performance in today's games than the current Athlon X2 generation, FUD Zilla claims:
In best case scenario you will gain 20 to 30 percent, but only in selected games and we are talking about clock to clock competition.
This will be AMD’s biggest problem and you already know that the Core 2 duo versus Core 2 Quad almost score the same performance in current games at the same clocks. Even 20 percent is unreal today.
Both Intel and AMD are hoping that in next generation games both Core 2 Quad and Phenom X4 quad cores are going to be significantly faster than Athlon X2, but I would really take this claim with a grain of salt.