I went to visit my foal's sire and found out he had been gelded. I talked to the guy and he said that pretty well right-away the horse lost his fleshy jowls. The guy seemed disappointed by it.
Me personally, I never cared for the fleshy jowl look, so I thought he looked great.
I think it has been proven that geldings get taller because the testosterone in an entire colt will close the growth plates earlier than a horse that has been deprived of the extra testosterone. But the difference in height is not that significant, only about an inch (I think it was The Horse
magazine that published the study).
I really think other aspects of it such as muscle mass are genetic. I have had several really chunky geldings. But I guess that begs the question, would they have been even chunkier as stallions? I don't know.
I gelded my QH/Fox Trotter colt at 5 months (he was and still is a handful, plus there was no reason to keep him a stallion). For the longest time he looked like a little Thoroughbred. All legs and a lean, sleek neck. Now at almost 17 months I've noticed he is starting to get kind of a thick neck on him. I would have been fine with the Thoroughbred look, but I do think my guy will end up looking more like a Quarter Horse after all.