Planning out PC purchases more than 2 months away is.... not very good use of time, especially with CES hitting in 3 weeks. I'm sure you'll have plenty of folks wanting to help you spend your money when you are ready but the PC market of March 2018 is going to look very different from today.
http://nvidia.custhelp.com/app/answers/detail/a_id/4176/~/what-is-hdr-and-how-do-i-enable-it
Get a copy of Unreal Dev Kit or Unity:
https://www.unrealengine.com/en-US/previous-versions
https://unity3d.com/
For the record I've got a great gaming PC and am spending 90% of my time right now on cheap Xbox games because HDR makes all the difference. And I play xbox on a 55" OLED. There's no comparable monitor i could get sub 30 inches that would work for me on PC. If you want to PC at 55+ inches tho...
SFF?
https://www.amazon.com/MSI-Aegis-VR7RE-036US-Keyboard-Included/dp/B06ZZ2GF82/ref=sr_1_1?ie=UTF8&qid=1512164061&sr=8-1&keywords=msi+aegis+1080
Very similar to what I have
I'd buy an Alienware with a single 1080/ 1080TI for about $2500 and call it a day, but that's just me. Anything more than $2500 is just a waste of money these days. Not sure what that translates to Canadollars.
https://www.pcmag.com/article2/0,2817,2393552,00.asp...
Spending 3+ grand for a PC with twin 1070s is pure crazy. There's nothing you can play today that doesn't look awesome on a 4k TV with a single 1070, but if you NEED more than that go for a single 1080TI.