I'd say you need 1250 to meet spec, considering 250 per card plus overhead. That Hercules is a Tier 3 PSU, stay away from it for extreme usage which I would definitely consider 4 290's extreme. You'd be better off with the EVGA which is a known quantity with a reliable reputation or the Corsair which has great reviews, for, well, a Corsair PSU. Guess they finally found a good oem.