1080 is still a great card, and does 4k gaming fairly well.
Have you thought about repasting it for possibly better temperatures, and overclocking it some more?
MSI Afterburner allows using the curve clocking feature to get more out of it, plus if you tap "L" after clocking a point on the curve, it locks the card to that voltage and frequency.
This trick allowed me to lock in 2088mhz and 1.1 volts on my 1080 TI, and its far more stable than 1.075 volts 2012mhz for some reason. I dont like being on the EDGE of stability, hence why Im running higher voltage.
But my gigabyte Aorus card has never seen above 55*C when the fans are at 100% (and silent by the way, great card)
In my opinion, unless you plan to buy an expensive high refresh rate 4K monitor, your 1080 card is going to work GREAT for you for at least a couple more years.
Get some time out of your purchase!! Have some fun gaming and think about it.