It's worth noting that I currently have 670SLI in my machine so would it be worth going to a 980 only?
I assume you were saying you might downgrade from a 980 Ti Hybrid to a 980 Hybrid?
Either way 980 Ti to 980 is a large downgrade, just so you know. That said at 1080p it should be a relatively smaller one. The best thing for you to do is go look at benchmarks for both cards at your resolution.