+1 the Coolermaster EPP's are over rated, rule of thumb is to subtract 100W to compare with a quality unit such as from Antec or Corsair.
My EPP550 just managed to power my 4850 and ran with the fan on all of the time indicating that it was running hot to feed the card at idle at. It had no hope running my 4890 but these are a ridiculously power hungry card.
These are rebranded power supplies and I think that they vary in origin across the range so try to find a review of your exact model with testing of the max load.
Also the 58xx series will consume less power than the 48xx but I would expect even a quality 500W to struggle.