Hi, you get about the same performance as your 580 from a GTX 970 and they are not to expensive.
The 980 is to expensive in my opinion.
In my latest benchmark the 500 and 900 cards profit from the file but nobody know why.
If your power supply and mobo support it use both cards, 900 for display/render and 580 for render.
Thanks for the links. Interesting reading. Not exactly the performance jump I’d expect from 4x the Cuda cores & higher clocks but faster non the less.
I’m actually looking at the EVGA GTX 980 SuperClocked version, not as expensive as the 980 Classified but very similar “stock” factory overclocking. I bought the 580 Classified with a view to over clocking it some but I found it to be so fast it could handle everything I wanted so never did.