VR stutter Oculus Rift CV1 from 5.4.4p1 upwards

Have tested up to latest version of Unity 5.5.1f1 today, and all versions after 5.4.3 stutters now in VR (same scene).

Performance is approximately the same in all versions of Unity in non-VR mode, but for some reason in VR it stutters.

Anyone that can help? much appriciated!