The SK 28 has an IC of 90mm which is quite a lot for a lens as wide as this one. (The Rodenstock 23 is a problem when it comes to movements - not sure if you had the Rodenstock in mind).If you go with a crop sensor, then you need to look at a SK 28 for your 24 equivalent. The downside is a really small IC so not much movement (a little on the crop sensor). But mostly that if you ever upgrade your back (and you will) it will just barely cover full-frame, and has heavy lens cast even on the P65+/IQ160, and so much cast on the IQ180 it won't correct.
Chris