Been looking at Titan X the last few days. Here is one article I came across on the topic:

https://timdettmers.wordpress.com/2014/08/14/which-gpu-for-d...

tl;dr: GTX Titan X = 0.35 GTX 680 = 0.35 AWS GPU instance (g2.2 and g2.8) = 0.33 GTX 960

GTX Titan X = 0.66 GTX 980 = 0.6 GTX 970 = 0.5 GTX Titan = 0.40 GTX 580

also: I was under the impression single precision was fine for most deep learning applications and double precision doesen't even have good support in most libraries but I guess it depends on the use case.