...look after the enviroment
If semtex is not going to use that much power, there really is no need to do a overhaul of the power supply.. and would just generate more heat than his old one has, which is what he's trying to avoid with all those fans.
Though you can get some good powersupplies that will exuast hot air out of the system, as well as from the powersupply, and if you do want one of these, I'd go for a 500Watt. I definetly wouldn't bother getting something as high as 600watts... hehe thats just a waste of energy...
Hope this guides you