Not sure if it's the case with their Polaris linup, but Gigabyte's Vega cards have a monumental rate of failure. I'd avoid them purely because of that. larger framebuffer goes a long way for newer games with heavier textures. Also worth bearing in mind that most GCN cards can be undervolted fairly well.
A 970/1060 3GB is slower (around RX 570 performance) and although the 1060 6GB is indeed comparable it isn't cheaper, cheapest I can see is £179.99 from Scan.
I'm not seeing a 6gb 1060 for less than this at the moment, looks like that only happens when an eBay code is live, the 3gb is a fair bit slower and going for a 970 means buying used and potentially running into vram issues in the future.
Surely better off with a cheap gtx 970 or a 3gb or even 6gb a gtx1060 for way less money and far less power consuption? Unless you are going mining in particular with it? Or am i missing a trick here?
Reasonable but despite the (budget) headset included I'd recommend a few quid more for the Sapphire card. Better quality heatsink/design.