The ATI HD 7770 from the Intel build is in my opinion quite crappy if you want to play games with good graphical settings, so I'd go for the AMD build and overclock the CPU. But to overclock you'd need to get an aftermarket cooler. The Coolermaster Hyper 212 EVO is only like 30$ and it does a good job, so save up a bit and buy it when you can. You'd be able to easily overclock to 4.2-4.5 ghz without a huge rise in temperature imho, and it would let you get more fps out of your HD 7850.
EDIT: If you'd change the ram from 1866 to 1600 mhz and drop the 2 case fans, you'd be quite close to the amount of cash needed for the Hyper 212 EVO.