You may have the compatible problem.
Because the i7-6850k was released on 5/31/2016, and according to the asrock site about the BIOS, 3.10 version for supporting 2016 Q2 coming new CPU.
So the MB will need the newer version BIOS 3.1 for the i7 6850K, and I guess the x99ws may not have it on. If you have the backup plan, like you can find the local PC shop where they can update the BIOS for you if the MB needs the BIOS update. Otherwise don't recommend to take the risk of buying the i7 6850k + x99ws.
The i7 3850K
http://www.cpu-world.com/CPUs/Core_i7/Intel-Core%20i7%20i7-6850K.html
BIOS and the cpu support list http://www.asrock.com/mb/Intel/X99%20WS/?cat=Download&os=BIOS