Kepler won't be far off. They ESTIMATED Q4 then put it back to Early 2012, i really dont think its gonna be 12 months or even 6 months for that matter. I reckon March at the latest. Also from what ive read about proposed specs it will be more powerful than 2 GTX580's.
Maverick123W you already have a single GTX580 that should eat through any game thats currently on the market at the resolution you currently have, save your money and wait or by March you will be kicking yourself. I'm sure you can cope with what you have till then....Remember, good things come to those who wait.