I would recommend going for the i5 processor. Up front the i3 and R7 would be better for gaming than the i5 with onboard graphics however your going to be upgrading that i3 rather quickly if you want to play any upcoming AAA title games. Rather than buy the i3 now and then buy the i5 or i7 a few months from now you would be better off to get the i5 now and get the R7 or R9 2xx later. Older graphics cards tend to drop in price more quickly than processors (the GPU market is much more competitive than the CPU market) so waiting for a few months and then getting the R7 (or better) will net you a better deal.
I say that your going to be upgrading the i3 sooner than you think because games are going more and more multithreaded and its only going to get worse once DX 12 becomes the standard. A lot of games are coming out with minimum requirements of i7 (however lets face it at least for now i5s can handle them just fine) i3s won't be able to keep up much longer you'll need at least a real quad core.