If you're not wanting to go with a Xeon and ECC for a full workstation, the motherboard really doesn't make a difference. There are no performance gains, and a lot of extreme high-end boards will offer features you won't need that are targeted to hardware enthusiasts, like on board power switches, larger VRM heatsinks etc... Just get something that you can comfortably afford that is validated to run your 6700k and I think you'll be good to go.