i5 is Quad core cpu and the i7 is Quad core as well but with hyber-threading which gives it the ability to act like a Octa Core cpu(8Cores), I am running a first gen i7 950 running at 3.3Ghz, and it runs UE4 perfectly fine, I have noticed that UE4 depends more on GPU power this time around, so get at least a GTX580,GTX660ti minimum but if your budget is strict then I recommend a GTX 750ti.