SLI 670 FTW results, why are they low

ive been trying to OC my 670's and im not very happy with the results, default clock 1006MHz oc'd to 1095 MHz memory 1552MHz to 1577MHz,
Heaven Benchmark v3.0 Basic

FPS: 24.7
Scores: 621
Min FPS: 4.2
Max FPS: 69.6
Hardware

Binary: Windows 32bit Visual C++ 1600 Release Mar 7 2012
Operating system: Windows 7 (build 7601, Service Pack 1) 64bit
CPU model: Intel(R) Core(TM) i7-3820 CPU @ 3.60GHz
CPU flags: 3599MHz MMX SSE SSE2 SSE3 SSSE3 SSE41 SSE42 HTT
GPU model: NVIDIA GeForce GTX 670 9.18.13.479 2048Mb
Settings

Render: direct3d11
Mode: 4800x900 8xAA fullscreen
Shaders: high
Textures: high
Filter: trilinear
Anisotropy: 16x
Occlusion: enabled
Refraction: enabled
Volumetric: enabled
Tessellation: extreme

3x EVGA GTX670 FTW
Asus Rampage IV Extreme
Corsair Vengenge
Custom water loop
i7 3820