I carried both around for a few months.
The 8.5's have a larger field of view, but more importantly in my opinion they have a greater depth of field. More of what you are viewing is in focus. But for some reason heat waves seem to affect the 8.5's more than the 10's.
The 10's obviously hold the edge in power and seemed to give me a couple more minutes of glassing in the morning and evening. I think this plays into the power edge also. I also feel that if you are going to own just one pair of glasses the 10's are a better choice.
The power to objective ratio is so close that it doesn't factor into the decision. I think I can hold the 8.5's steadier, but that could just be a mental thing.
From 0 to 400 yards with either glass I was getting the subject detail I wanted. From 400 to 700 yards the 10's out preformed the 8.5's in giving me subject detail. After 700 yards I was reaching for bigger glass anyway so there was no difference.
I picked the 8.5's. I liked the brightness and the depth of field. I also have other optics available if I need more power, and don't mind carrying a spotting scope or 15's.
If you are very weight conscience, I would pick the 10's and make due without a scope, or if this will be your only pair the 10's are a better choice in my opinion.
Most hunters I feel overlook the 8.5's, Either glass is great, and you will be happy with them.
