I react a lot, to both sex and pain. I'll moan, grunt, writhe, grind, and flat-out scream. I never know myself how much of it is a put-on. Probably some, because I can masturbate silently, but then again masturbation isn't at all the same sensation. On the other hand, when I'm having sex with someone else, none of my or my partner's concerns about family/neighbors/hotel management/"oh god my ears" will stop me once I start losing control.
Fortunately I do own a ball gag. Unfortunately, I can still get a couple hundred decibels through it. It's really just an aesthetic choice between "OHHHH GOOOODDDD" and "MMMM MMMMMF."
I love it when guys react, but usually they don't. Maybe a little right before orgasm, but I've never seen a guy do the full-on moaning thing I do. Pity. It would be hot as hell.
I thought this was a gendered difference, but upon starting to go to kinky sex clubs I've discovered that pretty much no one yowls the way I do unless there's an entire hand in them or they're having needles jammed through their nipples. And frankly, sometimes not even then. I'm amazed by the stoicism of some bottoms who have horrible things done to them and just stand there silently. I don't think they feel less pain than me, and sometimes I don't even think they have a higher tolerance than me, they just don't express it by hollering so damn much.
I think I also give a false impression of being much closer to my limit than I really am. I've had to explain more than once that "Aaaauugh" doesn't mean "stop." That's why we have safewords!
The funny thing is that when I get hurt in "real life" I'm not that big of a crybaby. I tend to laugh it off. But even if I could do that in a sexual context it probably wouldn't be a good idea.