Windows vs Linux & Mixed GPU performance
So I've been collating a few bits and pieces together and built myself a capable rig (well at least I think so), and it's come to deciding the operating system.

i7 6700k 4ghz
2 x GTX 1070
2 x R9 290x
Rm1000x psu

The mix of cards was a mistake on my part, accidentally hitting go on an eBay purchase before actually shopping around for 1070s. However having then sit around collecting dust vs in use in my rig I'd prefer to use them in the rig.

So my two questions are:
1. Is there a performance hit using hashcat in Linux vs hashcat in windows. (V3.20)

2. With mixed vendor GPU cards, would you recommend Windows or Linux being the easiest to get up and running?

Faffing about compiling and building kernel modules doesn't phase me (I use *nix on a daily basis) but I'm curious as to your experiences running mixed kit.

3rd question: is it even worth me running the mixed cards or should I just shove them on eBay and buy a 3rd GTX1070 from the proceeds?
1. I prefer windoze, but only because I don't know a whole lot about linux. I know enough to get around, but that's about it. Most seem to prefer linux.
2. I have never had luck mixing AMD/ATI cards with NVIDIA and having the drivers play nice, but YMMV.
3. 290x's run very hot, and pull a LOT of power. My suggestion-sell off the 290x's and get another 1070. The one 1070 will outperform the 2x 290x's and leave you room for another 1070 if you get the cash. (I am assuming these are reference design/founders edition cards you are speaking of).
Also make sure the case you pick has good airflow.
Thanks for the reply. Decided to stop faffing and just dive in this afternoon.

1. Decided what I wanted to do might just work straight out of the box on windows so went with that and it did.

2. Installed Intel drivers. Set bios to always use integrated graphics. Installed AMD card, installed AMD drivers, pulled AMD card installed nvidia cards and drivers, reinserted AMD card, bit of a heart in mouth moment as windows booted and showed nothing but black screen but it all came good in the end.

2. Case is a corsair 540 air. Plenty of airflow and making use of a single 290x for the time being alongside the other cards, it doesn't half whack out the heat but gpu temps are stable with 100% fans at 60c case is a cool 37c with ambient room temp being about 20c think you're right though, can see me flogging these soon to add a 1070. Sadly while all the cards are blowers, the 1070s aren't FE but this isn't a 24/7 rig and it was built on a premise of "whatever I build it'll be better than what I have now".