You need to run separate GPUs to achieve this though don't you?

You can run your host OS using the integrated graphics and assign the dedicated card to the Windows VM

I'm having a hard time finding any information about that. Anything you can point me to?

Ideally, I'd like to use 2x1080 (sli) with Windows KVM guest and then use the integrated graphics for Linux host.

google keyword : GPU passthrough

https://www.reddit.com/r/pcmasterrace/comments/3lno0t/gpu_pa...

There's a ton of guides, I found it useful to read a bunch of them and mentally prepare for the kind of stuff I should be doing.

Thanks! I've read up since the last post. Now I'm trying to decide if I can live without SLI.

The guide linked above was the same one I used. Honestly it took me quite a while to get it all working. I had to buy a separate soundcard since I wasn't able to get the one on the motherboard to pass through the audio correctly without static noise in it. Once I got the HTC Vive I ended up just going back to a dedicated Windows install and built a separate machine just for Linux stuff. Saved me lots of headache.

SLI is hard/maybe impossible with GPU pass-through. Let me know if you get it to work!

Not necessarily. I managed to get it working with a single GPU, by unbinding it from the host and binding it to the VM. Unfortunately it does mean that you have to stop X11 and all programs, and going back doesn't work (the GPU freezes the machine when the proprietary NVIDIA driver loads), but it's still better than dual-booting because background services continue to run. It certainly is easier with separate GPUs, though.

You can always have multiple VM's with gpu passthrough, so it's almost like dual boot kind of setup, but you can still run other things on the host. It works pretty well for me, only downside being that you're limited to single VM running at the time.

You can run multiple VM's at the same time as long as you have a separate GPU to assign for each VM. There are videos on Youtube of people demoing this.

I run Fedora 24 with no GUI, so I only have the one GPU. Technically my motherboard has a crappy GPU I could use.