It would be so much better if you were in bondage and someone else was clamping your nipples and giving you estim. When you do it yourself and it gets too much and begins to really hurt, you can take them off. If someone else clamps your tits and estims you, they decide when you have had enough. I love having my nipples tortured and estim on my cock. I played with someone once who put me in in bondage, put clover clamps on nipples, shoved a vibrating butt plug in my ass and estim on my cock. After I shot my load, he left the clamps on, turned up the vibrating butt plug and continued the estim. I was in a lot of pain but loved every minute of it.