A 970 is fine for 1080p, especially for Skyrim as it needs to be restricted to 60fps regardless of mods. Also, standing looking up Whiterun or Markarth will see frames of around 50fps with a 980Ti running at 40% or whatever... the game is bugged.
My advice would be to buy a 980Ti if you can afford it. They are awesome cards, and not only will you have room to manoeuvre with more demanding games in future, you'll also be well placed to up your resolution to 1440p without any trouble.
If a 970 is more aligned to your budget, it won't struggle at 1080p. You'll be getting a good boost with the extra 2GB of Vram and you'll be kissing goodbye to SLI issues and if memory serves me right when I moved from 670 SLI to a single 970 the grunt was a bit better and overall things were much smoother.