This question doesn't really make sense. AM3 CPUs have DDR2 and DDR3 memory controllers. AM2 CPUs do not. therefore to use DDR3 you must have an AM3 CPU. If you have an AM3 CPU there is no reason to buy an AM2+ board.
These overlaps only made sense if you wanted to drop.a new CPU in an old board. You wouldn't want to find an old board to pair with a newer CPU.
There were some AM2+ boards with DDR2 and DDR3 but again if you want to use DDR3 you must have a modern CPU and if you have a modern CPU there no reason to try and find and buy an expensive outdated board