I'd say the LEPA 1600 would be cutting it close. It might work, but for how long I don't know. I know guys that use that psu to power a whole rig with 6 7950s, but that's around 1400 watts.
I like to leave 15% breathing room. So for you that would be 1725watts. I would get dual 950's for that setup, personally.
Ok. But ow would be the load distribution? 2 5979 with mobo on one and one 5970 and 6990 from other ?
Also, i have one cx 600 lying around , may be i can use 3 of cards from lepa 1600 including a 6990 and one 5970 from cx 600, or may be 3 5970 from lepa and 6990 from cx 600?