Thanks all, lots of good advice, which has led me towards the 390 camp (rather than the 390X).
There seems to be a range of roughly £80 in the 390s at the moment - £229 for the PowerColor, up to £289 for the Asus Strix, with the MSI and Sapphire sat somewhere in the middle. Any thoughts on which is the best way to go, taking into account RMA/warranty service, extra features etc? Clocks seem to be fairly consistent across the board.
Powercolor is cheap for a reason.
Based on my dealings with them, I would never touch one again. If it works, great. If you actually have an issue, then I wish you luck.