Hello gsucci,
have you read the knowledge base article setting up the VR headset? Especially the bit where you tell SteamVR not to upscale your rendering?
The problem is that real world scenes that are generated in CAD are not highly optimized for VR unlike games. For your VR headset to run smoothly you need to render 90fps for 2 images. This setting of SteamVR does not make our life easier when we need to render even higher resolution.
If you want to get even more performance out of it, setting the slider to 70% has heeded some significant performance improvements with acceptable quality degradation.
Generally, unless you have the ultimate beast of a machine it is advisable to run VR in medium or draft, as a smooth frame rate is required to reduce motion induced sickness.
I hope this info helps.