I7-975 is still a great gaming cpu - all the money you would spend on mobo - put towards a kick-ass GPU!!! -Bruce
thats a pretty cool problem you have. I wouldn't worry about upgrading yet. (Nobody ever pays me in CPUs)
The i7-2600 is not compatible with an X58 motherboard. You will need a Sandy Bridge motherboard with an LGA 1155 socket to use that CPU. Ask whoever gave you the processor to return it and give you a better video card, such as a NVIDIA GeForce GTX 570 or AMD Radeon HD 6950, in exchange.