determined by the new Core i3 7350k's decently high stock clock speed and its ability to overclock(notice the K) i would recommend that you go for that as its lower wattage and more performance to the dollar as the 7350k runs at 60w and the i5 6400 at 91w. One of the main advantages of the i5 6400 is that it has 4 physical cores compared to the i3 7350k having 2 real cores and the same 4 threads as the i3 7350k. So, if you are going to be using lots of programs at once, id go for the i5 but if you want solid single program performance i would choose the i3 due to its several advantages over the i5