What's my bottleneck here?

[Nemesys]

So first, here's my setup:

Operating System: Windows 7 x64
Processor/CPU: Intel core i7 930 stably overclocked to 4.0ghz
Video Card/GPU: Nvidia GTX 560-ti Twin frozr II/OC
Memory/RAM: 4GB Corsair XMS3

The issue that I'm facing is with thew New Super Mario Bros. Wii. I'm trying to run the game with EFB to RAM with OpenGL and can only get about 45-50 fps, sometimes much less. The game runs fine with EFB to texture and everything else maxed out. I've been monitoring my cpu/gpu load during gameplay and with HT off a single core never goes above 70% and with HT on it never goes above 40%. GPU load is never higher than 35%. I have "prefer maximum performance" set in global variables through nvidia control panel, and a profile for dolphin just to be safe.

The only thing I can think of is it's possibly an issue with the RAM? This is supposed to be a triple channel set (3x2gb) but I found one of the DIMMs was causing issues, which testing with memtest86 confirmed. I would assume the RAM should be fine but can't think of anything else. Hopefully some of you smart cookies have some ideas

Thanks!

Edit: Specifying OpenGL. I can sometimes get 60fps with D3D but it's more like 52-57 consistently.