Need Help with Vid Card and psu

ok this is what i have currently(keep in mind all parts in box still)

-Intel Core i5 760 Quad Core Processor Lynnfield LGA1156 2.8GHZ 8MB Cache Retail Box

- Arctic Cooling Freezer 7 Pro REV.2 CPU Heatsink Cooler LGA1366 LGA1156 LGA775 AM2 AM3 W/ 92MM Fan 1

- G.SKILL F3-12800CL9D-4GBRL Ripjaws PC3-12800 4GB 2X2GB DDR3-1600 CL9-9-9-24 Core i5 1.5V Memory Kit -50895

-Western Digital Caviar Black 1TB SATA3 6GB/S 7200RPM 64MB Cache 3.5IN Dual Proc Hard Drive OEM

-ASUS P7P55D-E LX LGA1156 P55 ATX DDR3 1PCI-E16 4PCI-E1 2PCI USB3.0 SATA 6GB Sound GBLAN Motherboard

-OCZ ModXStream Pro 600W ATX 20/24PIN SLI Ready Modular Cables 135mm Fan Active PFC Power Supply

-Coolermaster Haf 922 Mid Tower ATX Case Black 5X5.25 5X3.5INT Front Audio USB eSATA No PSU

-Samsung SH-S223C 22X DVD Writer SATA Black OEM

-Microsoft Windows 7 Home Premium Edition 64BIT DVD OEM

-Acer H243H BMID 24" LCD Monitor

- and possibly add my multi card reader from old pc

main purpose pc, gaming, playing poker bit surfing, watchinng movies

so my main question is....i have around $300 to pop for the vid card won't be going sli, so one card it is, i was thinking the msi 470gtx twin frozer or is an ati chipset one of equivalent better, example say a 6870 or 5850?......and is my power supply sufficient?, i bought the psu in a haste as was a doorcrasher thing and couldnt refuse the price, but after doing more research , little leary if i oc my processor and vid card and mem abit

thx in advance