If wearing a jonny (rubber), I’d say 75% of the time I don't cum... it's not just down to sensation, they just destroy the moment / intimacy for me just the smell of them pisses me off - lol!
Granted, they had different sensitive spots and liked different pressure, but it's all relative. If you have any kind of sexual experience you will find what she likes and it won't take too long.....
You just have to be in to them enough to find out what pleases them.....that's it.