600W is enough for your crossfire. For gaming more than 4G of RAM doesn't help.
Ya, i do more than gaming. I use Photoshop, FRAPS, Vegas, 3dsmax, and I do a bit off multi-tasking while programming in C/C++/Python/Java and other sorts of web development.
Are you sure 600W is enough?? I want to be sure before I make a final decision on what PSU.