The situation with the availability of Cambo parts and accessories may be different in The Netherlands, but there's so much Sinar stuff out there second hand that as with Armin, Sinar makes the most sense for me as a studio camera. I haven't needed to rent LF lenses, but lenses are most available for rental on Sinar lensboards in many major cities.
I would think that the main functional attractions, availability of parts aside, of a Sinar P/P2 over a Cambo would be the asymmetric movements and DOF calculator. The rear tilt and swing axes on a Sinar P are marked on the groundglass, so you can quickly and easily find the focal plane and measure the tilt and swing angles on the rear standard and use the scales to transfer those movements to the front standard as desired. Of course it is possible to work without these gizmos, but they can be time savers when you need to work quickly or if you have a complicated tabletop setup.