no one mentioned this, and maybe I got things wrong, but python 3 is significantly slower than python 2. at least this is certainly true using spyder (maybe its not in other cases)

laptop py 2.7 (4 cores 3ghz, 16 gb ram) vs desktop py 3.5(6 cores 4.5 ghz, 64 gb ram) - both windows. When I am running my models for kaggle competitions, my laptop usually finishes first by about 20% total time, unless the model I am running can take advantage of my GPU.

edit: I never figured out why, but if I generate a submission with 3.5x, 75% of the time its accuracy is significantly worse.