I would say to buy the best you can afford. They will both last quite a few years before needing an upgrade. The x99 chips have a much thicker pcb currently, so there is less chance of the pcb flexing. Aside from that, it will mostly be preference and then consideration for what you will be coding.

I would think it would come down to what you do most..gaming? Single core performance is better on skylake for the most part.
 
Multi-core and threading? X99 kills the Z170...
 
But that's my standpoint.
 
 

thanks for the answers. i know that these are pretty general questions. What are the typical tasks that an x99 setup are really better at than a z170? 

If you are coding, it may help with processing whatever you are coding. Since you only said coding and not what you are doing with it, then it is still a mystery of which will be best.

Are you coding videos, are you coding software? You need to be specific to get the best answers.

things are always going to get "better and faster" after every new model / platform release
 
I personally is using the Skylake as my daily computer its a less" exhausted platform" and OC higher on the memory within a reasonable VSA with 5820K...
 
I have a 5820K chip that's very nice, i have booted up 5ghz on air below 1,4v, and its running stable at 4600mhz 1,23v  24/7
My other chips was in the neighborhood of 4300mhz 1,3v  (sold them)
 
5820K at 4600 or 6700K at 4600
 
6700k at 4600mhz is fully enough for what i use the computer for today, even though the 5820K is faster in MC benchmarks, the 6700K feels more "snappy"..
 
 I like the "old way" better, with the regulators not present on the CPU PCB......
 
its a matter of taste i guess
 

 
 

I was in the same boat as you a couple weeks ago. I went X99. The reason was I wanted more pcie lanes. I'm running an M.2 and will have 1 GPU for now, possibly a second later.