With chrome 59+ you can also eliminate the need for xvfb by running it headless.
Our behat suite of 1800 scenarios and 19000 steps takes just over 60 minutes to run in Chrome 58 with selenium and xfvb. With chrome 60 headless it takes less than 18 minutes.
https://gitlab.com/DMore/chrome-mink-driver
Any feedback and contributions would be greatly appreciated.