if only for gaming, 1600x is enough for your build
there is no merit going for 1800x if only for gaming as Ryzen 7 series is more for workstation
Ryzen 2 is said to be little more powerful, more efficient and cheaper than current Ryzen (even tho they use the same AM4 socket, and X370 and co. need BIOS update for later compatibility)
and yes, if you gonna gaming only, i7 8700k is ofc better suggestion for you