Yeah the VEGA 64 competes most often with the GTX 1080. It does cost a bit more than some of the 1080's, but it's liquid cooled so will run quiet and cool. Gigabyte warranty also means UK RMA, which is great.
The only slight reservation I have about that system is the CPU, due to its low clock speed. However, you can just overclock the 1700 and if necessary get a new CPU until 2020 - as AMD is supporting the AM4 socket 'til then. But at 3440x1440p you would be more GPU bound anyway, so the CPU is less of a factor overall.
Looks like there is a VEGA/CPU/Mobo/RAM bundle on the horizon, "available soon" according to the link:
https://www.overclockers.co.uk/rx-v...gaming-16gb-3200mhz-8-pack-ram-bu-02p-gi.html