You really dont know how they will react. Kids are all different. When my dd was 3 she was 42"+. Yes, she is a tall one too. But even though it is tough on them when they are too small and a CM turns them away, its worse when the CM doesnt catch it when they are too short.
We were on our first family trip to
Disneyland. We got in early and the crowd was light so the first place we went was Space Mountain. Excited that we could run thru the turnstyle and get on a big ride with no waiting we grabbed dd and ran to catch up with a train that was half full and just about to leave. I had dd in my arms when we ran up jumped on and within seconds of getting in the bars came down(that was before they referbished it, when you sat side by side with only a lap bar to hold you in) . DD was beside me and the lapbar came down to the level of my lap, but was loose on hers. We took off very quickly and very quickly I realized that I must have misread the height requirement of the ride. She loosely slid around in the seat. I held tight to her but was sure she would slip loose. After getting off the ride and looking at the height it was at that time 48" not 42". I do take responsibility, but I do wish one of the CMs were doing their job and would have measured her.
That said, the scary ride on Space Mountain just wet DDs appetite for wild rides. But funny thing is, she was scared to death of the dark rides. Now 11 still doesnt like a couple, especially Snow White and Mr Toads Wild Ride, but loves everything else.
Other DD(6), when she was younger, would go on a coaster or thrill ride (even Splash Mountain) and come off screaming, crying and telling us never to make her do that again. Five minutes later she would be laughing and giggling and begging to do it again. Now she will go on everything and luckily she is just 48".
Those of you that have childeren that very close, dd(6) was really close on one of our trips to DL. A fraction of an inch doesnt probably doesnt matter.