Yes, I've read the science supplied by people in here. That doesn't really mean anything to me. When Apple says its 2.5X brighter I expect it to be noticeably brighter, and its really not.
The couple of videos I’ve seen show a very noticeable difference outside in bright light or sunlight, where the S5 AOD hits its maximum and the S6 goes beyond that. In those videos the S6 AOD is noticeably brighter than the maxed out S5.
As expected of course, under conditions where the S5 AOD isn’t maxed out, the two appear of similar intensity. i.e. usual indoor conditions, both day and evening.
I’ve still not decided to upgrade, so I’ve not seen this in person of course.
Clearly you have both on hand, and you see what you see. Fortunately Apple has a good return policy and you can avail yourself of that if the watch doesn’t meet your expectations.