Leaving 6 cores enabled or 2 cores gives out the same performance.

Average use of 6 cores is 33%, 2/6 cores in a six core processor. (real 6 cores phenom 2(thuban), not hyperthreading or vishera)

Average use of 4 cores is 50%, 2/4 cores in a four core processor.

IO of SSD remains low, Average use of gpu doesnt go higher than around 45%, low resolution and low settings or high res and ultra settings, fps remains pratically the same.