i5-750: 7 years old 45nm, 95W TDP, 2.66GHz, cores 4/4, socket LGA 1156, DDR3-1333, 16 PCIe 2.0 lanes
i3-6100: 1 year old 14nm, 51W TDP, 3.7GHz, cores 2/4, socket LGA 1151, DDR3-1600/DDR4-2133, 16 PCIe 3.0 lanes
Unless you need to put something in old LGA-1156 motherboard that you already own or can get for free, no way you should even think about i5-750. Plus at same cost as i3-6100 it is a scam anyway.