First of all, thank you. This is a fantastic post.
I don't have much to say except that these are all very beautiful - someday I must visit the PP Museum in Geneva.
The 5110 and later models are great but in all honesty, they pale beside these! There is something about the proportions of the dials that changed (more legible, less attractive). And while the 5131 centre dial is lovely, I disagree strongly with the choice of typeface for the cities and maker's name on the bezel. Still, I could put up with a 5110P...there remains a poetry to it...
Best
E.