So it lags when you launch steamvr? Have you by any chance enabled SS in steamvr, or are part of the steamvr beta? Do you have asynchronous reprojection on and interleaved reprojection… If you do disable interleaved reprojection (settings+performance). Also turn SS to 1.0 is steamvr settings.
In latest piplay, use the render slider and put it to 1.0 to start with… With a 1080 is should be super smooth… If it is move the render slider to the right… Upto about 2.5 to start with… If still fluid keep going right till you feel minor stutter then drop down 1notch
As helio said, if you have Klite installed please uninstalled it as piplay has its own version. If you do uninstal Klite you may need to reinstall piplay again to get the right Klite for pimax.
Also use July 2017 Nvidia drivers as they do not cause micro stutter in game, and have the best experience.
If you are connecting directly to your GPU, make sure there are no hdmi extensions or USB extensions between hmd and pc. and let us know if you are using adapters to change the output type I. E. Dvi, Dp, mini Dp etc… Also if possible ensure you’re external monitor does not use hdmi as it will utilize a channel from your GPU slowing the hmd down.