Now that's something of a dilemma, but I'd suggest the only point of variations may be the size and the decibel level, plus the number of moving parts.
In stuff like this, it's usually very very minute that we find a difference in specs, it's just these added goodies and the few bucks here and there that make the difference.
Yeah!! Not to mention the OCing factor......
The MSI hawk is known for its overclock ability (superior cooling/bundled software). XFX has the best warranty on the market, double lifetime (US). Both of them are great cards from good manufacturers. It is more a question of what you want.
If you are not overclocking, there really is no reason to pay more for a better cooling solution. The stock cooler is very adequate. If you ARE overclocking the HAWK is the better option. You may ALSO want to consider the HIS with IceQ cooling. HIS is very know for these model of coolers and their big fat heatpipes. I've always liked them.