I have 1080 in my gaming machine, and a Vega 56 in my Linux primary machine.
I favored team red for my linux machine, due to drivers.
In my gaming machine, which I built in july 2016, I have a 1080 FTW, because it was the king of the hill at the time 
As for your case, either the 1080 or vega 64 will push a lot of pixels. IMO it comes down to the price of the cards, and if you somewhere in the future would like a monitor with either freesync or g-sync. When you buy your gpu it kinda decide what kind of monitor you want - if you want adaptive refresh rate.
My 1080 do 3440x1440 @ 100 hz no problem.
And for pass trough, the Nvidia driver can detects if it’s in a VM, and it will disable itself. There is a workaround. But doing pass trough with the Vega 64 will be less of a hassle.
There is a guide (of sorts) here on one who passed through a 1080 to a windows vm: Ryzen Virtualization Success (GTX 1080ti passthrough with Windows 10 client)