I'm not looking for a specific set up, just clues as to what to look for to determine if an instability might be a shortcoming of the airframe, or just poor prop selection.

Yes, trial and error will work, but I'd really like to avoid carrying 4 or 5 props per plane to every maiden flight. I'm sure that's what the "big boys" do, but many of them have prop manufacturers backing them. I pay retail, and sometimes plus shipping too...[&o]