How about we compare R700 (2xRV770) to GTX 280 SLI?
Price is a bit different though I guess lol.
BTW, some of you really need to understand GPU architecture a bit better. R700 is not more efficient than a design based on a single giant GPU would be. At least, not for pure 3D performance. The fastest GPU design, due to how parallel 3D rendering is, is always a single GPU. Dual GPUs waste RAM and have to deal with inefficiencies caused by trying to split the tasks and communicate via a pathetically slow bridge chip. There is extra hardware and hardware performing redundant tasks. And the drivers have to be specially set up for every game basically (this is conveniently ignored by most people for some reason.)
The problem is that manufacturing technology can not cope with mega huge GPUs. That is why GT200 can't clock as high as G92. The bigger the chip gets with more transistors, the hotter it is and the more complex it becomes to make it stable at higher clock speeds. If you look back at how early GPUs barely needed fans to today's ridiculous furnaces, you see that manufacturing is way behind what competition has pushed GPUs to become.
R700 and 9800GX2 are designed to overcome manufacturing inadequacies in the only way possible. They also conveniently allow an entire lineup to be based mainly on a single GPU design. It's just important to realize that this is not the optimum way to go for performance.
Also, realize that there is potential for a refreshed GT200 to be vastly faster. If they shrink it down and tweak it, and this allows it to clock up decently higher, a dual GT250 (or whatever) could be a lot faster than R700.