£550 Budget Gaming/Rendering PC Build

Hey Guys, trying to get a build done in time for Christmas and I have 2 really big problems when I have been making the build. I could either go for an i5 2500K + HD 7770 or an i3-3220 + GTX 660. I have been really thinking about this and I can't decide. I am going to be playing games suck as AC3,Arma 2,Metro 2033 at 1920 x 1080 but I can go down a bit if I have to. I will probably be replacing the CPU once Haswell comes out because prices might drop over a period of time. If someone could make a perfect build it would be great.

EDIT: Nothing Needed included(OS,Monitor etc)

EDIT: Changed GPU from HD 7870 to GTX 660 to save costs