I will through in my .02, and let the "pro's" beat up on me, lol.
I bought my first thermal last January, and everybody told me I was looking at getting positive ID below 200, some even said 100.
I have zero issue's ID'ing past 500 yards. Last year I had a pack of coyotes run in and break through the treeline about 600 yards from me, and I had zero issues knowing it was coyotes heading my way. I was absolutely certain. One of my properties I hunt, spans to 600 yards before it hits the tree line, I watch raccoons, deer, and coyotes run out of that tree line all the time.
Obviously the closer they get, the better the image. I know a lot of people give examples of like animals (bear cub vs hog), I don't have animals like that where I live. When I hunt, all I see are coons, coyotes, and deer. So being able to distinguish between what I'm looking at is easy. Maybe I would have a different point of view if I lived in those states.
I will also make another statement, in no way shape or form will I take a 500 yard shot on an animal. I don't posses those skills to make accurate shots that far. Just want to make that statement before people jump on me for shooting that far when they don't think I can ID that far. I usually won't shoot past 200, not because I can't ID further, because I want to be able to put a lethal shot on the animal I am shooting and not just wounding it.