Can you - yes. Should you - absolutely not. What are you trying to achieve by having two completely different video cards? You can't run them in any form of CrossFire or SLI configuration. You will get no added power from having the two.
You could get two of the same of either kind (2 x 980Ti or 2x295x2) and run them using the provided multi-GPU solution, and that should easily push 4K.