There was a limited run of something called a Mars 2, which is a full double 580 that can be heavilly overclocked. A water cooled version was also available, but you were looking at I think $1700 per card. A pair of Mars 2 cards, a couple of top end PSU's, and a ferocious motherboard, RAM, and CPU will get you a formidable system, as well as in the poor house.
Steve