Here is a focal length visualizer
which allows you to compare the image produced with either a 35mm camera or an RZ with film.
Given the three aspect ratios (6:7, 3:2, 4:3) there is no single "correct" answer to what the equivalent will be as it matters a lot whether you are matching the vertical or horizontal.
If you're working with a value added dealer you could do a test shoot with such a back before making your decision (note this is a biased suggestion as we are such a dealer). There is no substitute to actually trying it in image making.