Hi bibendum,
Hmmm..interesting choice you got there...both are very different watches for different occasions. One is more of a dress watch and the other is a diver. No prizes for guessing which is which.
I cant say much on the DeVille as I have not handled or seen it. But I can share my opinion on the PO 8500. Just picked mine up today 42 mm orange numerals on SS bracelet. First impression..its a hefty watch. But it sits nicely on the wrist. Wears very confortable..even with its weight.. its been like 5 hours I since it on my wrist..I can honestly say I dont feel the weight at all by now.
Also, its a rather thick watch, I can see problems wearing cuff shirts over it. But it would look great with a T-shirt. I indend it to be my daily beater, so IMHO, the P.O will look not too out of place on weekdays (in a suit if required) or weekends (casual). I find the 45.5 dial looks better...but too bad I got a small wrist..hence couldnt carry the big watch look.
The finishing is absolutely spot on..and the see through case is a real novelty. Its hard to find a diver with a transparent back...for me only minor issue is the crown which I find its a bit difficult to turn. Also, for calibre 8500, no quick set dates but there is quick set hour hand. You have to manual set the date by moving the hours. A bit of a pain, but no real biggy if you wear it daily. Yet to test its accurancy since its so new..but heck its COSC certified, so shoudnt be that far off.
Overall, the P.O is fantastic watch by itself. I wont go to the extend to say its on par with a Submariner, but $-$ its a lot of watch for the money. Its has better tech, looks great.. and being substantially cheaper than a Sub..what more can one ask..except its not a Rollie..

Will post pics once I get around to it...