I don't have an 8500 to compare it to and there's no display back to admire it through, but I have no issues with my 2500. Last worn before Christmas after sitting in the box for a few years..... lost all of 1 second in the day that I wore it.
Not sure that's any help in your decision.
EDIT: Specifics, dear boy; specifics ?.... It's a 2500D.
Further EDIT: Regarding thickness - I used to go for big chunky watches but not any more; as I've 'grown up' (debatable !) I definitely lean more towards slimmer watches. I don't even need them to slip under a cuff (polo shirt at work) and rarely wear a shirt & tie, I just prefer them thinner these days.
The extra 3mm of the 8500 in this case would be a non-starter for me. If it were me, I'd be going for the sleeker model - Less is more, and all that.