Steam VR is a pain in the arse if you use a Rift. However, even though you might need to run Steam to access the game, you do not need to run Steam VR;
Make sure Steam VR is off. Run OpenComposite, click on 'Switch to OpenComposite' and close the app.
Run the Occulus launcher.
Now run the game.
Enjoy an extra 10fps and all that added smoothness.....