Don't buy enermax, PLS. I've lost all faith in then as a quality PSU manufacturer, even though I use 1000watt DxX PSU. IF I opened my PSU up and showed you the insides...
I think the corsair unit is a nice unit.
When it comes to Crossfire with 2900XT, or 4870x2, it is best to tr yto stay away form quad-rail units, unless 1000W or greater.