Core Clock in 8800GT Worth it?

Ok there are like 3 different evga 8800gt out there. The only difference seems to be to core clocks. How much real world (FPS) difference will these 50mhz increases make in gaming?

The BGF goes to 675 and the Gigabit go to 700. I like evgas warrenty, but whats the real difference here and does it justify cost?

Thank Again Everyone

Xipo