Sorry if I’m late to the party on one: I have a 980 at home and a 970 at work. Difference is - there is no difference, everything runs almost identically. Any minor differences can probably be traced back to the rest of the hardware being different.
One way or the other, the 900 series cards are utter monsters, and seemingly impossible to get either of them hot too! You’re pretty much clutching at straws when it comes to comparing them, they’ll both last as long as each other and give you the same amount of smiles!