You should be fine. The test system they used in this review uses an i7 920 and similar components to your system. Bottom line, under full load it only used 461. So I believe you should be fine with your 750W PSU.
"GeForce GTX 590 - On your average system the card requires you to have a 700 Watt power supply unit.
GeForce GTX 590 SLI - On your average system the card requires you to have a 1000+ Watt power supply unit."