The dual GPU setup means I can rack up 6 (or even
GPUs without need for extenders.
Hash for Hash 5970 has superior performance/watt than a 5870 due to less duplicated components. Wattage is about 15% less at same hashrate.
Thats because by default its clocked at only 725 MHz instead of 850 for the 5870 and the vcore is therefore be dropped to 1.05v rather than 1.16v for the 5870. Im pretty sure a 5870 can do that just as easily, considering my 5850s can do 800+ at 1v. Underclocking will increase your perf/w if you also drop voltage, that goes for any card. It will decrease your performance /$ though. But having 2 cards also means you can tweak clock and voltage per card.
Anyway, not saying 5970s arent great cards, particularly if the prices are like that in US, but saying nothing comes close seems somewhat exaggerated and depending on how you clock and volt them, local prices, the rest of the system, how much luck you have with them breaking down (*), 5870s can be more cost and power efficient.
My 2 cents.
(*) Stumbled upon this:
ATI Failure Rate
28.57% Sapphire Radeon HD 5970 2GB
20.83% XFX Radeon HD 5850 1GB
17.14% Asus Radeon HD 5870 1GB V2
14.29% MSI Radeon HD 5870 1GB
10.00% XFX Radeon HD 5870 1GB
7.41% PowerColor Radeon HD5750 1GB Silent
6.67% MSI Radeon HD 5850 1GB
5.10% XFX Radeon HD 5770 1GB
0.00% XFX Radeon HD 4770 512MB
0.00% MSI Radeon HD 6870 1GB
0.00% Asus Radeon HD 5850 1GB
0.00% Sapphire Radeon HD 5870 2GB Eyefinity 6
0.00% Asus Radeon HD 5870 1GB
0.00% XFX Radeon HD 5750 1GB
0.00% Asus Radeon HD 6850 1GB
0.00% XFX Radeon HD 5670 512MBhttp://www.reddit.com/r/gaming/comments/ek3ie/ati_vs_nvidia/