RAM speed is one of the very last performance differentiators, a few percentage points is the best you could hope for in real terms, often it'll be sub percentage points. Its a horrrible way to blow money on a rig if you want the best performance for your money. If money's no object or you're a hardcore, professional OCer, sure why not go for it. Otherwise get some deent branded DDR2 1066 and be happy that you didn't buy $200 worth of epeen and bugger all else.
All those Phenom iis are created on the same process, and a 3ghz full quad core balck edition will be one of the best picks of the bunch, so it should have no problems with overclocking. So if they both overclock to the same range all you've got is that .2ghz clock speed bump, which means the absolute best boost you could ver hope for would be a 6.67% increase in performance but that's only in situations where raw clock speed is the single one bottleneck, which in the real world, it very, very rarely is.
So, we're talking, overal,l a 5% performance boost (and that's a generous estiamte) but that's only when yo're CPU bound, which is very rare in modern games. Which means in the vast number of games the difference is well, nothing, or at least nothing you'd notice, that's for sure. If you want a few extra 3Dmarks to inflate your epeen, then, by all means go ahead.