I would like to give some real information on the "vibration" issue with the Sinar Hy6 raised here. I am not sure what Hy6 body you have had in your hands, but pre-production models and prototypes did not have the latest and final built and firmware updates like the production units.
The Hy6 has a completely new direct mirror drive concept allowing for vibration free releases.
The camera has been designed with the task in mind to be used with our multishot backs (4- or 16-shot modes) and assure a vibration-free shooting. This is the case with the Hy6.
On the other hand, I have a very good friend of mine owing a Contax and who used it for some reproduction work with a SB 54 multishot: he had problems with vibrations and had to modify it with some felt to damp down the vibrations. This photographer is also member on this and other forums and has reported this problem elsewhere.
So the Contax might be alright concerning vibrations in the single shot mode, but not with multishot. On the contrary, I can assure you that the current Hy6 with the newest FW are absolutely perfect for the use of a multishot back.