Hmm...
That's an interesing problem. There are alot of variables in cranking pressure and it rarely directly relates to a CR. But if those variables were removed (ie same cam, bore x stroke, etc. as you mentioned) you may be able to make a rough estimate. But I think you might need more than two points to extrapolate from since it will more than likely be a curve of some order. I might ask one of my lecturers about it (I doubt they will have any answers though, they have been pretty dissapointing so far!)