Well I want to get an Intel motherboard (LGA1155 preferably for i7 2600k and overclocking) with CrossfireX 6990s which are dual gpu cards which would be considered as 4 cards on a motherboard and I don't know a motherboard that supports quad crossfire. Also I saw that one 6990 at full load consumes 554w!!!! if i wanna get 2 and i want to overclock the cpu and gpus what psu will i need?
Before you buy any PSU you should read accurate, objective PSU reviews at reputable sites such as www.jonnyguru.com or www.hardwaresecrets.com on the EXACT model PSU that you are interested in as some brands have good and poor quality PSUs.
You can also get an accurate rating of how much PSU power is required for your current or future system at the PSU calculator link below. Once you know the total PSU watts required then you need to confirm that the 12v rail has enough amps. to support your Vid card(s) and the rest of the PC system.
There are several websites that show the Vid card power consumption in watts. Divide the watts by 12 to determine the amps. required on the 12v rail(s). Add 15 amps for the rest of the PC on the 12v rail and you now know the Minimum total 12v rail amps required under full load. It's best to have at least 5-10 amps. reserve on the 12v rail available under full load so the PSU is not loaded to 100%.