No mention of k80's k40's...
K80s and K40s have a K. That's two generations old. We are currently on P and about to be V. If you think K80s are good, you are far far behind the times in machine learning. A single 1080Ti even in a 4U server outperforms 2 K80s.
We found that the GeForces tend to burn out when under heavy load, whereas we've not had a single Tesla series ever burn out.