I'm not the original author of this site, but here is interactive performance chart of GPU's and you can find both there, the chart is based on several benchmarks from trusted reviewers: http://existenz.php5.sk/GPU/index.php
In terms of raw gpu performance the 295 is quite a bit more powerful, but it is a crossfire setup. Personally I would never spend the money for a 980 ti if I had a 295.
I'm not the original author of this site, but here is interactive performance chart of GPU's and you can find both there, the chart is based on several benchmarks from trusted reviewers: http://existenz.php5.sk/GPU/index.php