Both can run everything, but I3 has only 2 cores so there would be some fps drops, I would take the I5 with 2666Mhz ram or higher, but it's not necessary
i3 is scary good, but more and more games are wanting more and more cores. IMHO, though, if you get an i5-6400, you might as well pay the slight incrwse to get a 6500 instead, especially since BCLK overclock has gone away