Replacing a 1060 with a 980ti is like replacing a 1060 with a 1070 - there's almost no point. The 1060 is newer than the 980ti and will last you longer.
The 980ti was the king back in 2015, but it doesn't hold a candle to the Pascal cards. Plus, $300 for a 980ti is an immediate red flag for me. I'd advise you viciously check on the card and test it in-person before ever considering buying it. In the case that it really is a perfectly fine 980ti for $300, you still wasted a lot of time and effort for slightly better framerates, a higher electric bill, more fan noise, and a worse prognosis. It's just not worth it in my opinion.
See what the next (or the next-next) generation of cards has in store. The notion of "upgrading" your card intra-generation is asymptotic and viciously cyclical. Enjoy your card while you can, and upgrade either when prices REALLY drop or when a new card is able to take the place of the 1060 but at much higher performance and efficiency. Do you see what I'm getting at?