OK MP looks amazing i got everything maxed out, motion blur switched off, now ...
VRAM usage 1.1GB, no worries here, GPU usage 90 - 100%, should be ok, ...
When i was playing MP it was terrible, especially when explosions were happening, very bad stuttering, ...
WTF? Do i have to reduce some in-game graphics settings?
gtx 580 OCed
i5 760 @3.8
8GB gaming ram, 1800
850 PSU,

Gonna try bringing the GPU's memory clock back down to default right now ...

Putting the VRAM back to original clocks sorted the low fps.