i think just a bit above average is perfect, but (being a slut, lol) i do enjoy variety and can appreciate a monster cock now and then that's really going to put me through it. and i don't know what it is, but in my time i have encountered more large or even very large cocks than smaller ones...i don't believe that's reflective of society at large, maybe i'm just lucky that way, lol.
in college i was with a guy so large that he actually TORE my cervical lining. if that sounds painful and horrifying, it was!! and the crazy thing is he wasn't even very rough, just tapping it from the back and he pulls out and it looks like a bit of my insides are out on the floor! sorry to be graphic but we're all grown-ups here. i thought i was mortally injured or something but he was totally calm, like, "yeah, this has happened before." i was like WTF?!?!!? he was apparently used to ripping girls apart.
maybe it's the masochist in me or the submissive pleaser in me or some combination of the two, but even after experiences like that i do look forward to those challenging experiences. especially when you consider the fact that most of the men who are that large have never felt free to truly relax and just use their cock however comes naturally...i met a few who confessed they had never even fully penetrated a woman before. so of course that tugs at my subbie heart strings and i just have to do all i can to take it like a champ.