I'm also running Insider Fast and driving two 4K Monitors while docked
Sorry to go off-topic again on that comment, but may I ask how your monitors are connected? Is one off the mini-DP port on the SP and the other on the dock, or are they daisy chained, or ... ?
I'm on the verge of ordering a SP 2017 and that is one question I had: how to keep my current dual-monitor configuration at home.
Thanks!
PS: If I have further questions after reading your response, I'll start a new thread.