I have a small wrist. I am ok as long as the lugs do not extend past the edge of my wrist. That is 50mm lug to lug for me. My Speedmaster 57 is 41.5, but wears large because the lug to lug is 50mm. I have 42mm watches that are 48mm lug to lug. They definitely look large, but I am ok with it.One other thought I had was this:
Most people have no idea how big their watch actually looks on their wrist because they only look at it close up when telling the time. Which, I suppose, is important in how it makes you feel. But much like how shoes don't look the same when you look down at them versus how others see them, I'd wager the vast majority of people who think their "small" wrists can't take even a 40-42mm watch because of how giant it looks close up when telling the time would be amazed to see how completely fine it looks seen from a distance—i.e. how other people see it.
We did some family portraits on the beach last year, I wore my 41.5mm Aqua Terra, which before then I occasionally wondered about being too big for my average-sized wrist. But then seeing the photos made me realize the truth—it's fine.