To the guys with 970s, these are bstocks which are what they are but are certed by EVGA:

https://www.evga.com/products/produc...set=GTX+980+Ti

$400 +-

Run two cards:
Monitors to the 970
Computation to the 980ti.

You will knock it out of the park. They run off the same software without conflict.

Mixing generations of cards is more trouble than it is worth. This is a simple relatively cheap solution.