Here is a set of comparisons between a Intel G3258 and a X4-860K in games.
The G3250@ stock 3.2 handily beats the X4-860K.
The i3-4170 has two cores using the same architecture @3.7 plus two extra hyperthreads.
http://www.techspot.com/review/1017-best-budget-gaming-cpu/
One other consideration, there are no good cpu upgrades available for the required motherboard.
Any Intel lga1150 motherboard can support a i5 or i7 cpu upgrade.
You can get a quite hefty graphics upgrade with a GTX750ti which does not need a aux 6 pin power connector and takes it's power from the X16 graphics card slot.
300w or possibly less is ok.