I think for a similar price, you could get a slightly better card with the GTX 750 ti. It's also really low power. You'll be able to play anything with that card so long as you keep down power-hungry settings. Take a look:
http://gpuboss.com/gpus/Radeon-R7-260X-vs-GeForce-GTX-7...
As for the question, "How many fps more will I get with this card?" I can't really answer that, and no one can answer it across the board. It depends on too many things. All you can really do is look at performance graphs to tell you the comparative advantages. The only time you can really answer how many more fps you'll get with a certain card is when you run the same exact scene on each card, using the same settings, running on the same system. Luckily that's exactly what benchmarks do. Look at some. All said and done, though, you're looking at a card that's about 10% to 15% faster.