I'm glad you found the guide for using Unity with R3 helpful. I am currently experimenting with integrating the DLL file of the new RealSense SDK 2.0 with Unity.
Unfortunately, it is a known issue that face tracking has problems in R3 when the Essentials module and Face module are used together. As development of the face tracking module for Windows has ceased, the only remedy recommended by Intel is to develop face tracking applications in the R2 SDK. There used to be an article about it in the permanent 'sticky' messages at the top of the forum front page.
Are you using an F200 camera with R3? If so, a 4th generation processor would be fine. The SR300 camera desires at least a 6th generation processor though.