W3tan

Hey I had the same i5-6600k and the board I have is asus z170-e. I started 4.4ghz@1.325 volt. Stable. Tried 4.5ghz but crashed @1.355 volt so I decided to stay at 4.4ghz. 
 
Then I tried to lower the voltage and finally settled at 4.4ghz@1.31 volt. The cooler I have is NH-D15 and temp was around 70c running real bench. 
 
Just my experience with 6600k and I hope you have a better chip than mine! 

Bought an EVGA 1070 FTW about a month ago. Very annoying coil whine. Looked up online and many other EVGA 1070 owners have similar issue... EVGA customer service is excellent though. 

You could SLI three and OC all three on 850W.
 
The 750W G2 sounds like it's perfect for you. Go for it.

If you're the kind of person who replaces their CPU every 4-6 years or so and you keep your temperatures in check, anything at 1.4 V or less will most likely be just fine. I say "most likely" because while I've never seen or heard of a non-defective processor fail so soon when overvolted that high, it's not technically ruled out as an impossibility.

I am using Fractal design arc midi r2. Good build quality, reasonable price and very spacious for a mid tower. I think you can mount 240mm rads top or front. 
 

I am using Fractal design arc midi r2. Good build quality, reasonable price and very spacious for a mid tower. I think you can mount 240mm rads top or front. 
 

I bought an EVGA 1070 FTW last month. Excellent performance as it boosts up and stays around 1950mhz. Thermal wise it hovers around 72C with fan at 40%. 
 
The only con is that it has some high pitch and annoying coil whine. I contacted EVGA and they provided lots of guidance and follow up to reduce the coil whine. They also said I can RMA the card if I want to. 
 
Just want to share my experience with you. My FTW card is not perfect but EVGA's customer service is excellent.

At the time of purchase there's a promotion on FTW cards and both cards were selling for $599 Canadian dollar. 
 
I was lucky and unlucky at the same time I guess...