The evga SC would be better than the XFX alpha dog. Both may hit the same clocks, but out of the box, the evga is 650/1900 vs 680/1600. The stock evga at 550/1600 would also be able to hit the same clocks (luck of draw for exact clocks for all 3)
And the evga variable speed fan is a plus for anyone concerned about noise. With the XFX, it's a 2 pin fan, so no way to control voltage/RPM in software. You have to feed it less voltage yourself (like rigging it to a variable voltage zalman fanmate or fixed voltage reducer, or feed it 5v or 7v from a molex, etc. )
If you don't already have COD4 and don't mind noise or taking the steps to control it yourself, then grab the XFX. The XFX for $99 shipped free with COD4 is a better bargain IMO than the alpha dog, but it does have slower mem for the $20 savings.