So I ended up buying the 980, it will arrive in 2 weeks or so. Right now, I think Nvidia + G-sync is the better option for me after weighing up all the info.
So while future free-sync monitors will no doubt be cheaper and ebay will no doubt have more sales in future, who knows when that will be, and I don't want to wait around forever. I speculate that the fury (non-X) will beat the GTX 980 for around the same price when it comes out, but then I wouldn't be able to get it on sale.
I think most Asus parts are just plain overpriced outside the US. For example, the ROG Swift monitor is $50 more expensive than the Acer XB270hu over here, despite having a TN panel type instead of IPS. Asus non-reference video cards are also the most expensive compared to gigabyte, MSI, etc. So that might be why the free-sync MG279Q one is barely any cheaper than the acer G-sync.
And it would have been cool to get a 980Ti or Fury X, but this will still be a massive upgrade over my old ATI HD 5850! No point spending too much either cause after 14nm or whatever node parts come out with HBM everything may change.