Similar size cases: 46mm v 46.2mm for the 5004. I have tried to measure the dials but there is 1 mm or a fraction of a 1 mm difference. However, the perception, to my eyes, is the Big Pilot has more free "real estate" on the dial and looks bigger. An ideal Big Pilot would drop the power reserve on the dial and look even more like the B-Uhr.
Thank you very much for your help. From your comments it looks as if the classic big pilot looks to be a little bit bigger even though in reality it is not.