The issue with my SLI setup is mainly noise and heat, no surprise from 970's. So just going from dual to a single GPU will lower the noise and heat.
With the reference 980 Ti. Heat will be reduced yes, but noise will not.
You'll have to invest more into an aftermarket cooler to lower the noise. The cheapest option being Artic Accelero Xtreme IV/III. The more expensive being Kraken G10 + AIO water cooler. The best but most expensive option being building a custom water loop + getting an block for it.
For your need, the artic accelero xtreme should be plenty enough. They go for around 80 USD. You'll get to overclock the 980 Ti (to performance near SLI 970's) while having very quiet operation.