I've still got my 1080, I decided not to sell as like you say the value has sunk a wee bit more than I had anticipated and to be honest it's a cracking card in terms of how it clocks (2Ghz) and the quality of the cooler. I bought it at £30 more than the price it is going for now, so in that respect I genuinely don't have any buyers remorse.
What has prompted the step up talk is a wee bit bizarre. I was reading through the BBC news app when I noticed that Bitcoin has soared in price. I had a paper wallet in the bottom of my sock drawer that had 0.23BTC and it had been lying there for 2.5 years!

Back then, the value of it was about £65. Yesterday, it was worth £240
https://bitinfocharts.com/bitcoin/address/12gETL3jXG873uRzjRTzRnUN1nF4MPDcsh
Anyway, I don't want to be transferring my bank details around for Bitcoin trades so I decided to buy the most saleable GPU for the value I was holding at a store that accepts Bitcoin. My initial intention was to sell on straight away, but now I'm pondering whether to hold on to it for a wee while in case I do decide to switch to the 1080ti - hence the step up queries.
I'm going to hold off and see what the benchmarks are like because I want a 30% increase over what I have if I'm to move to the 1080ti. If that's the case, then I'm buying the 1080ti, and two lucky MM surfers will pick up a 1060 & 1080 at very good rates.
Finding the Bitcoin has pretty much justified the purchase to me as it was money I never had, but as I say I really want to see benchmarks because if they aren't up to scratch I'll just punt the 1060 and keep the 1080.