The cooling will be better, but the single fan edition will not be worse in performance, just higher in temperatures. You'll have to turn the fan up a bit to keep the card cool, hence overclocking headroom will be reduced. In a dual fan card, the card will stay cool at lower fan speeds, allowing for better overclocking. The difference, after overclocking the dual fan, would be ~2-3 FPS in most games, but that's just an approximate number. The point is that the difference will be minor, maybe even negligible(depends heavily on various factors like GPU, game, settings, resolution, etc).