I am buying a new graphics cars, an upgrade from my HD 6770, and I decided to buy a HD 7950. But I am not sure what brand to get. I saw Sapphire and Powercolor versions on Newegg and I really like those (mostly because of the lower price). I am on a super tight budget and I am not sure which one to get. What do you think? Oh and will a OCZ 550W 80+ Bronze PSU be enough for this?