If you're after quiet, very definitely best to wait until ~September anyway. The 1070 is due soon but it takes a little time for best custom cards to come out/pricing and availability to sort itself out!
Its mostly guesswork for some of it:
1070 - very soon indeed but as above best to wait if not desperate. 150 TDP so there will be some very, very quiet models from some of the after market people.
Definitely faster than a 290, but won't destroy it performance wise. 50 per cent maybe?! £350 ish(? guess work, they've given a dollar value but that conversion is very random at times )
Polaris 10 - availability unknown, but definitely meant to be 'soon'. If they aren't there by September something will have gone horribly wrong at Global Foundries. May get a few cards up to 1070 performance/power draw, the bulk likely to be lower speed but also lower power draw, price etc.
So you could maybe get +20% performance and a really low power draw that way for around 200ish. Similar deal with NV's roughly similar 'smaller than 1070' cards which should be coming out round Autumn.
The case for waiting a full year?
There will be top cards faster than the 1080 out there from both sides (absolutely certain), but they'll be pricey and power hungry. Most likely effect would be the 1070/80 (and/or AMD equiv) dropping in price. So good chances of either saving ~£100 or getting 20-30% more performance at current 1070 prices.
Projecting from NV's very consistent historic trends, we're due mid range Volta in 2-2.5 years which may well be ~70% above the current 1070/80 at the same kind of power draw.
Those (and any AMD response) should be the cards the truly meet your first post, but plenty of good options in the mean time too Just depends what you want to do.