An i3 6100 will provide a great experience in the vast majority of games. There are a handful where an i5 6500 will perform noticeably better, but whether it justifies the extra cost is contentious.
EDIT: As uguv says, you need an older 1150 CPU, such as the i3 4160, if you're going to use an 1150 board. The i3 6100 uses the newer 1151 socket.