8xxx are just re-branded 7xxx cards. You want to wait for the 9xxx cards, which are going to be faster. They're supposed to have a higher core count, wider memory bandwidth, and faster clocks all around, which looks like a recipe for some serious alt-coin mining.
That is what i`ve heard also. I also read that the releasedate of the 9xxx series is in late september. I doubt it will be a major gamechanger, but i`m still kinda looking forward to it.