http://www.guru3d.com/article/radeon-hd-6990-review
System Wattage with GPU in FULL Stress = 526W (i7-965 @ 3.75)
http://www.anandtech.com/show/4209/amds-radeon-hd-6990-the-new-single-card-king/18
Load Power Consumption in Crysis = 491W
Load Power Consumption in Furmark = 550W
(i7 920 @ 3.2)
The answer is that these numbers are cutting it way too close to the rated wattage of your PSU. You'd want a 750W unit.
Another line of reasoning: 6990 consumes more power than 6950 Crossfire. If you ran 6950 Crossfire, you'd need four PCIe connectors - but no 550W power supplies ever comes with four PCIe connectors. Most 650W don't either. But all quality 750W units do.
Not gunna run furmark or overclock, but look at these results:
http://www.hardwarecanucks.com/foru...s/41404-amd-radeon-hd-6990-4gb-review-21.html
469 Watts in 1hr 3DMark w/ i7 920 @ 4ghz.
http://www.tomshardware.com/reviews/radeon-hd-6990-antilles-crossfire,2878-15.html
Max @ ~430W in Metro at stock with a decently OC'ed 130W CPU i7990X@ 4ghz.
So what are you saying? Do you want me to tell you your PSU is enough for 6990, and you won't accept any other answer?
I'm telling you, it's not a good idea to run 6990 off of a 550W unit. You're looking at over 80 percent power consumption in games, and games don't even stress your system to the max. As a rule of thumb you shouldn't cross 80 percent with your system stressed to the max. Running a PSU at such high stress for long periods of time will wear it out faster.
Guru3D recommends 750W, AMD recommends 750W, and that's what makes sense to me as well.
Can I ask you why you're considering a 6990; how much would you be paying for it? What resolution do you game at and what is your current graphics card?
I don't deny that it would work, but that doesn't mean it's a good idea.
OP: I think it comes down to this: That PSU will work and will work fine if you don't OC anything. If you have the money, a bigger PSU isn't a terrible thing but if money is tight, honestly, it should work fine.
Would it really break the bank to just go to a 650w and be done with it?
