Interesting thing I notice is that the 5970 is, in fact, two 5870s put together but with lowered clock speeds to adjust for voltage/temperature. It is possible to OC a 5970 to the effect of two 5870s and more with the right cooling.
All of this is according to newegg reviews and tomshardware articles though and I have no personal experience with it. Just found it interesting that at that price you could get two 5970s for nearly twice the graphical power.
3200 shader processors. There isn't much more we need to say about the brutal rendering muscle that characterizes the world's fastest graphics card, the Radeon HD 5970. With two Radeon HD 5870 GPUs onboard, the only things we can complain about are scant availability and an extremely high price tag. Availability has improved over time; the price not so much. But if you're in the market for this card, price probably isn't an issue.