Bad Ram or Incompatible MB?

Well,

I just purchased twin Corsair XMS2 PC-6400 DDR2 800 ram and it is performing quite badly. I have upgraded from Corsair Value Select DDR2-667 and am having quite a time with it. What I failed to realize when purchasing the new ram is that this XMS2 stuff has a voltage rating of 2.1v. Now, correct me if I'm wrong, but I have heard (OCZ) that the Asus P5B mb has problems with higher voltage rams (1.95+).

Here is what is happening:

1. The PC posts with no problems.

2. Windows takes a noticeably longer time to load.

3. When playing Gears of War: it will work fine for about a min or so and then it will become and unbelievably bad stutter fest, usually associated with not having enough Ram to buffer all the textures and what not (btw, the game runs on full detail @ 1680x1050 at a constant 45-60 FPS with old ram and minimal ram hitching)

4. Using Vista's DOS based Memory test tool through 2 full cycles of extended tests, it finds no errors.

No BSODs (usually associated with bad ram) or anything that would lead one to believe that the ram is in-fact bad. Any insights would be appreciated. Would hate to have to pay the restocking fee on the ram, or worse (maybe better) yet, shell out for a new MB (P5K-P5W maybe).

Thanks