600w should be fine so long as its a good brand. Cooler master have some good models, but overall they make a mix of poor, average and good psu's depending on the model. If you stick to brands like Antec, Corsair, Seasonic or XFX you cant really go wrong. I always stay away from any companies budget range and try to find a review of the psu i am looking at before i buy. the review must properly test under FULL load and test for noise, ripple etc. some reviewers just slap a psu in a test system, put a multimeter on it and say "it worked" and give it 5 stars, while a proper reviewer will load up all the rails with a load tester and the psu may crash and burn. Jonnyguru and Hardware Secrets are 2 of the best review sites for PSU's, and also give you a lot of good info about psu's in general. Another rule of thumb with psu's, if the price is too good to be true, then it is probably a cheap nasty product.