I might be a little biased since I own 2 2GB GTX 650 Ti BOOST SLI. I like AMD's cards, too, but I prefer SLI and I think NVidia's drivers are a tad bit more sturdy (no Direct 3D device has failed and recovered problems). You should have a good quality 750w Power Supply like my Cooler Master 750W GXII. It'll run 2 GTX 780-Ti SLI or 2 Radeon R9 290X XFire no problem and only cost me $79.99. Don't limit yourself with that pitiful power supply of yours.
Core i5 2500K @ 4.5GHz (45x100) 1.350v-Asus P8Z68-V/Gen3 (BIOS 3402)-16GB Kingston VR DDR3-1333Mhz @ 1600MHz 1.65v-2 EVGA GTX 760 2GB (1212/7600) ACX-750w Cooler Master GXII-RealTek on-board sound-Intel Onboard 1Gb Ethernet-Rogers Cable Internet 6.6MB/second-2TB Seagate 7200 SATA 6 HD-3TB SeaGate USB 3.0 EHD-22" Samsung SyncMaster 2253BW 1680x1050 67Htz-Windows 7 HP 64-bit SP1