Right now there is no reason whatsoever to go with an i7-6850K CPU or an X99 motherboard, especially if the street prices in your area for those components are still on the high side (remember, the i7-6850K has only six cores and 12 threads), since both components are now EOL and obsolesced. If you're going to be doing 4k often you will want at least an i7-8700K with a Z370 motherboard, or an i7-7820K CPU with an X299 motherboard, or an AMD Ryzen 7 series CPU with a compatible AM4 socket motherboard. All of those platforms that I suggested require DDR4 system RAM.
And with those platforms your originally considered GTX 1060 is OK; however, I'd go higher up to a GTX 1070 or 1080 for any of those three platforms that I suggested.
Thanks Randall. It's a bigger budget upgrade that you suggest, but i totally take your point and perhaps i should just be patient and go to a x299 system in about a year.
No problem. It's just that at this point the older X99 platform is simply overpriced because even the 6850K costs more than the 8700K/Z370 platform while it doesn't perform any faster or better than the newer platform.