Unlikely you need that much power. 375 is TDP. It is the max power the card is designed for. You won't hit 375 in real life even at 100% GPU load 24/7. On the 5970 I pull about ~260W from the wall per card. 3 cards running off a 1250W PS. Total draw @ wall is normally around 930W.
Take a look at benchmarks for 6990 from various sites to get an idea of real world power draw.
http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/41404-amd-radeon-hd-6990-4gb-review-21.html
If you want to go w/ dual power supplies I would go with maybe 700W - 800W units (1400 - 1600W combined should be more than enough). Of course a 2kW of power isn't going to hurt anything it just may mean you are overspending some.
Thanks for your comment but I know what TDP is.
So if you noticed I took TDP value in order to Scale the PSU, not a precise value.
Actually MB+CPU + etc will also not consume at Maximum possible levels.
Also almost all common commercial PSU's will be at their Top of efficiency at 50% Load ... hence the double 1000W ... I know ... I know .. it is only a 2% at most difference on the efficiency curve ... but to me it matters. Likely over a 5 year period pays for the price difference to non-optimal configuration ... and after those 5 years I am sure the PSU was not pushed to the limits so longevity is also an issue.
Also besides the PSU's being at their peak efficiency at 50% load there is also the issues of electric spikes on the Electrical installation you are running your equipment.
My gear will not be in my home. It will be running on a industrial type of facility where electricity is much cheaper, there is 24/7 security, no noise for the neighbours and so on ...
So apart from having peak protection gear on my electric circuit I must make sure my PSU's are not at the very brink of taking 3500US$ /Each with them when a possible and un-controllable peak comes along.
The facility in question does have a lot of heavy power machines ... so all care is important.
If something I really do not care to pay a bit more for the PSU. It is one of the components I do like to bet in terms of proper dimension and quality.
Regards.