MichaelC[AP Moderator]
21984
Hi Frank. I am recommending the Diver, despite my general preference for the Royal Oak line.
I have enjoyed Royal Oaks for many years on my wrist. The 15400 reference is simply a "miss" on my wrist. I have tried it on a few times, it just does not evoke the correct proportions for a Royal Oak. I would personally purchase a 37mm 15450 before I would spend on the 41mm model.
The Diver, on the other hand, is a superbly executed Royal Oak Offshore with classic proportions for the model. I have worn Divers, and they are "just right".
Good luck making the decision that is best for your wrist.
PS, yes, both watches utilize the 3120 Caliber.