There are DDDR3 boards for the Skylake platform but its counter useful. The 6300 is a waste of money, the 6100 is basically the same thing. The 8350/70 has the benefit of overclocking and in some more demanding titles will play better. An i3 6100 is a pretty solid chip and games well, and there is also a good reason to take a FX8370 with the wraith cooler for some good overclocks.
I would take the i3 as you have a little upgrade path to a quad at a later stage, with the FX you are on a dead end socket even though it is a lot of fun to play around with them.