Neoseeker translated a bunch of information regarding AMD's future Radeon HD 5870 GPU from a German website. All this information could be nothing more than pure speculation, so take it with a grain of salt.
According to the site, the next high-end GPU from ATI will be a 40nm part with a die of only 205mm², which would be about 20 percent smaller than the RV770. It's believed the "Radeon HD 5870" will be a DirectX 11 GPU, with 25 percent more shaders than the Radeon HD 4870 and a computing power of 1.5 teraFLOPS, 50 percent more than the Radeon HD 4870. The memory is said to be GDDR5, with a 512-bit memory bus, resulting in a memory bandwidth of 150-160GB/s.
And here is where things get really interesting. The HD 5870 supposedly uses some sort of cooling that ATI hasn't tried before. And thanks in part to the small size of the GPU, the HD 5870 X2 is going not have two separate GPU's -- instead it will be two RV770 cores stacked on top of each other, sort of like Pentium-D style.
If this is the case, theoretically you could put three HD5870X2 into one motherboard, giving you like six times the power of one of HD5870 -- now that'd be performance. Of course, back in the real world, things don't scale very well after 3 GPU's are CrossFire'd. But who knows, maybe ATI will work some CrossFireX magic up, who knows.