I literally went and checked my GTX 970 box and screamed in agony afterwards.
CURSE YOU NVIDIAAAAAAAAAAAAAAAAAA.
Then again, most boards don't even support SLI and those that support it comes with SLI bridges.
On-Topic:
A single powerful GPU is better overall(for me) than with two lower tier ones.
So basically GTX 980 Ti all the wayyyyyy.