No.
5970, although a good card with dual GPUs, awesome for gaming, SUCK ASS for mining.
You cannot crack MSI Afterburner using them. Which means you cannot underclock the memory or overclock the core very much.
What the hell are you talking about? Where did you get such bogus info?
MSI AB works just fine w/ 5970 but cgminer works even better. Driver (no catalyst control center) + SDK 2.1 + cgminer = optimal perfromance. You don't need anything else. cgminer can set clocks, fans, and voltages. Memclock runs stable down to 150Mhz. I usually run at 820/190 (found 190 is faster by 1 MH/s or so than 150) but I baby them. 840 is possible with aggressive cooling and 870 with watercooling.
Mh/s is roughly 450 per 1 Ghz which is exactly the same as HD 5870. Obviously you can't clock a 5970 to 1 Ghz so running at 820 MHz gets 82% of that, at 870 Mhz it is 87% of that, etc.
You are better off getting two 5850s and over clocking the HELL out of those. That is basically what a 5970 is. Two 5850s but I would rather have two 5850s ANY DAY over 1 5970.
Well a 5850 has a different core than a 5870/5890. It has 1440 shaders vs 1600. It also has inferior cooling system and VRMs which are only capable of lower amperage. Still you can drive a 5850 pretty hard but it has a lower performance per watt (mainly due to use of a chopped down chip & lower MH/s per board). A properly tuned 3x5970 dedicated rig can get >2.5 MH/W (3x5970 @ 820/190/1.05V = 2.25 GH/s @ 870W) at stock voltage. If/when the network becomes more efficient, one can undervolting and underclock to get >4 MH/W (4x5970 @ 600/190/0.90V = 2.2 GH/s @ 530W).
On edit: fixed a couple typos.