Another possible one (even though it is getting old slowly
is the one I bought, AMD HD 7990 (2 HD 7970 in a single card). It did pretty good on the building test I just ran.
It is going as strong as the Titan X (actually slightly faster).
Device 1 performance: 192.642 million samples/sec (CPU)
Device 2 performance: 869.168 million samples/sec (Tahiti) (1 half of the card)
Device 3 performance: 847.02 million samples/sec (Tahiti) (the other half of the card)
Total performance: 1908.83 million samples/sec
So the actual card itself did 1716 million samples/sec
The only problem is that it is pretty thick so even though you can place 2 cards next to each other, there will be almost no space for ventilation on 1 of them.
Leo