5970 would probably have the same power consumption as two 5870's, the two gpu's on the 5970 would have seperate ram chips for the two gpus, two different sets of VRM's(maybe) and the GPU's themselves are somewhat the same as the 5870's. So you probably would not notice too much of a power consumption difference.
As far as temperature, TBQH, having two seperate cards or one card with two GPU's it's going to generate pretty much the same amount of heat. Only difference with the 5970, you have room to install a PCI slot cooler or a directional fan to get better airflow to it. Or install multiple expansion cards, I like my 12 port SATA controller card, I need the 16 ports for my 14 x 2 terabyte drives :P As you can see with two 5870's, that's somewhat difficult to do :P
Yes the 5970 will be a few degrees warmer at high load, but TBQH it isn't going to be enough to warrant a OMG it's too hot!!!! My 4850x2 runs 4 degrees warmer than two seperate 4850's in crossfire, so whoop dee freakin doo.
The 400$ would have been better spent in the bankz generating interest so you can buy the next gen ATI card when and if Fermi get's released this year. We all know ATI is going to throw something out or cut prices to directly compete with nVidia's Fermi :P
Edited by Scroll_Lock88, 19 February 2010 - 12:44 PM.