The rendering frame rate of their system leaves a lot to be desired. The VR hardware looks good for their needs and usage, but that frame rate totally kills the immersion. That's inexcusable in this day and age - people have better gaming rigs than that. My guess is they have a very poorly optimized modeling system that has to pull data from whatever CAD systems they use.
1) The framerate doesn't need to be optimized as they're not going for immersion, but rather the ability to look things over from novel angles in a semi natural way. In fact immersion might run counter to their goals in this situation.
2) The car models are probably extremely detailed and overmeshed even to guarantee that the model has high physical fidelity. A large amount of the performance in games that is lost in CAD is due to geometry bandwidth.
3) Also X-Ray mode implies some pretty interesting alpha blending type effects so they're probably losing most of their Z-Culling and line drawing also isn't as optimized in graphics hardware as most people don't use it. It's actually a selling point on several CAD workstation graphics cards that they accelerate line drawing.
4) The motion capture system tracking their hands and heads also probably introduces some level of system latency.