I never encountered Ventuz being unstable when dealing with heavy polygon count models. The frame rate just dropped and dropped and dropped ...
I created a touchscreen application for a car manufacturer about a year ago and there 15 car models at the same time - including reflections.
Here is a screenshot:

- Audi Motor Show Touchscreen Application Snapshot
Since the cars were never visible on the entire screen and since the screen was only 42" the resolution/quality of the models did not have to be too high. I think they were somewhere around 150K-200K polygons per model. So the most important question you have to ask is: How big will the models be displayed and how big is the screen you are displaying them on? Let's assume the worst possible situation. Fullscreen on a gigantic screen. The most important factor then would be RAM. Main Memory needs to be very high and especially your GPU memory needs to be high so you do not have to load the models and everything can be stored in memory. At least that is my experience.
I would maybe create two version of the models. One lower-poly version with reduced details for the menu selection and the high-poly version for the configurator/showroom parts. You only show one high-poly model at a time so you won't have any problems.
Very important: Avoid SLI or Crossfire. Do not use Graphics cards with Dual GPUs on one board. You might think that the large amount of RAM those cards have is great but in fact each GPU core takes only half and Ventuz3 does not work well with SLI/Crossfire. So no AMD Radeon HD 7990 or GeForce 690 cards. Those are a no go. Since I am a true supporter for nVidia because their cards are reliable, stable and exceptionally fast I would recommend a GeForce Titan. If you have to output across seveveral screens you should go with Quadro K5000. The Quadro card is less powerful than the Titan but allows for easy multi-monitor setups. Especially with Ventuz4 that will be a very potent combination from what I hear.