I've heard lots of people say that neutered cats dont' grow so big and some people avoid early neutering in order to ensure the cat grows to it's full potential size wise, but there is actually evidence to the contrary. I have a study bookmarked at home that compared the size of cats neutered early (paediatric neutering), about 6 months, and later. The group that were neutered early actually grew to the biggest size. I dont think neutering affects skeletal structure at all, but the hormones that entire males have tend to give them a heavier set, jowly look in the face. I may be wrong, but I think that when those cats are eventually neutered and the hormones get out of the systme, the face shape will gradually revert to a less jowly shape.
Jaffa and Mosi are both big cats and they were both neutered at 5 months.