HD6970s in Crossfire > HD 6990 > GTX590.

HD6970s in Crossfire are also pretty much the same as GTX580s in SLI. Superior Crossfire scaling and all that. It becomes even more apparent if you start doing three-card setups.

Speaking of SLI: AMD and company have released the 990FX motherboard chipset. The draw? It supports both SLI and Crossfire, so now you don't have to go all AMD if you want an AMD CPU. This is good news for me, since now I can choose 580s for my build this September. Oh, these are also AM3b (also called AM3+) motherboards, so they support the full featureset of upcoming AMD FX line of CPUs (Bulldozer/Zambezi). If you are rocking an AM3 board, you can still use the new CPUs, you just don't get the power and frequency management features or the HT 3.1 capability.