Take it from me a Corsair AX1500i does the job with 4-Way SLI, since I ran 4x EVGA Titan X SC's. And bere in mind this was also running triple screen surround resolutions of 7680x1440 which really pushed the cards.
After reading the purpose of your system, i'm left scratching my head why on earth you would need 4-Way SLI in the first place. You don't need it, actually nobody does. It's really just pointless outside of benchmarking.