OCC has published a review on the AMD Athlon II X2 255, X3 440, X4 635, Phenom II X2 555, and X4 910e

Overall the new processors offer a great price to performance ratio and I would recommend them to anyone in the market for a new processor. I would not say go out and toss away an already good processor for a small performance gain, but for a fresh start these are a good buy. If you are on a limited budget and want to overclock, the best out of what you got for $99 the Phenom II X2 555 will offer you great performance on stock and even better when overclocked. With the new silicon used for this processor, you should be able to get above 4GHz often allowing you for the best price to performance out of the bunch.

AMD Athlon II X2 255, X3 440, X4 635, Phenom II X2 555, and X4 910e Review