The Open-Source NVIDIA Linux Driver Continued Evolving In 2015
The lack of change for the GTX 650 results seem to indicate there were no broad optimizations this year in performance but for the other graphics cards their rise in performance is just thanks to being able to manually re-clock higher.
Hopefully in 2016 we'll see Kepler re-clocking stabilized and some form of dynamic re-clocking enabled by default.