THats what im saying, if your pushing your two 6990s like you should and you have a good system overclocking it, running strong, you want a 1k wall thermaltake at minimum, anything less is just going to die, no reason to push it, now if you run just the cards, basic system you can get away with it, but if your trying to keep it running 24/7 for awhile, then the thermaltake 1000 watt is the best option for the price.  15k are overkill but pretty expensive.  RIGHT NOW THE  Corsair HX1050 is out replacing the 1000 watt and is always a good choice.