I've run an am3 x3 720be in both am2 and am3 mobos. Really wasn't much of a difference in the memory between fast ddr2 and mainstream ddr3. In other words the chip ran great and has a very good memory controller.
I was just using it till the amd 7750 I had ordered for the am2 box came in. When I swapped that I noticed a big difference. The phenom series was a dog, but the phenom ii is a really good chip in am2 or am3.