a large cock would damage the ass more so than the pussy. the ass is not designed/built for penetration. so i think only a really long/thick wang would cause any permanent damage to the pussy. maybe a guy with a 14" length and 7.5" girth or something. lol. but then again, a new born baby is bigger than practically all penises, and this causes no lasting damage really.
Thank God most women have orgasms while giving birth.
Now on topic: I dated this girl for a while, and me (being aware of my MASSIVE HUGE ENORMOUS length) didn't penetrate as deep. But she started pulling me deeper so I hit her cervix. I could see on her face she had pain. She told me she liked that feeling of me hitting her deepest spots, but after getting to know her in bed, i noticed she liked it better if i didnt do it all of the time. So what she wanted was me, every so many thrusts, hitting her cervix. But if you do it to much, the vagina gets sore.
Btw, i never caused injuries, stiff muscles from time to time but thats all...