If you go with i5-4460 then you're getting DDR3 RAM that usually runs at speeds of 1333 Mhz.
With i5-6400, you're getting DDR4 RAM that runs on speeds of 2133 Mhz.
While DDR4 is more expensive than DDR3, the speed gain is also quite considerable.
If you're unsure what MoBo to use with your i5-6400 then here's some further reading,
link:
http://www.tomshardware.com/reviews/best-motherboards,3984.html
Note: Z170 chipset MoBos are for the OC of the K-series CPU. Since your CPU is non-K, there isn't much point going with Z170 chipset. Go with H110, B150 or H170 chipset instead.
And as far as going with i5-4460 or i5-6400, here's a comparison between the two,
link:
http://cpu.userbenchmark.com/Compare/Intel-Core-i5-4460-vs-Intel-Core-i5-6400/2310vs3512
I'd go with i5-6400 build. It's much newer and it uses much faster DDR4 RAM. Add the GTX 1060 and you're playing today's games @ 1080p in high/ultra settings with 60+ FPS.