InsideHW.com has compared performances of AMD Phenom II X4 810 with DDR3 and DDR2 memory

Newest K10 core was from start designed to support DDR3 memory standard, but from unknown reasons (to us) AMD decided to disable that support for 65nm revisions of this CPU. Even first Deneb 45nm cores had disabled support for DDR3 memory. Deneb cores that have DDR3 support are the same C2 revision that initially appeared on Socket AM2/AM2+. Same mistake with transition to new memory standard AMD didn't want to repeat so new AM3 CPUs are backwards compatible with AM2/AM2+ motherboards. If you have old AM2 motherboard that supports Phenom CPUs, new Phenom X4 810, X3 720 or any other AM3 CPUs can be plugged in and everything will work flawlessly with "good old" DDR2 memory that you already have.

AMD Phenom II X4 810: DDR3 vs. DDR2