I must admit, I have had the 15450 on my wrist several times, and I am quite impressed with it. It exudes AP's quality and refinement, and I honestly think the proportions on the watch are perfect. I am also a big fan of the Caliber 3120. It is robust, easy winding, offers a long power reserve, and a very crisp rapid date adjuster with a safety mechanism to protect against accidental damage. If it fits your wrist correctly (and it sounds like it definitely will), I see it as the perfect every day Royal Oak.
Here is a link to a thread from last year with some nice photos:
ap.watchprosite.com
Perhaps some 14790 owners will weigh in as well. Keep us posted on your decision; I know you will be pleased with either.