I will weigh in here and say form personal experience there is definitely a point - which may be very different from woman to woman - where any more length will just not fit no matter the level of arousal, time of the month, etc. (Though these factors are extremely important before this point is reached of course)
For those who are not in the know, I have a very petite girlfriend. I was certain at some times in the past she’s taken most if not all of my length, but I’ve found that to be shaky via my favourite: experimentation! :D
I recently got her a jelly dildo which is 10”x5.75” - the closest to my size I could find (of course I didn’t want one bigger, and I foolishly assumed she’d use the majority of the length). I wanted to see just how much would fit into her and even after orgasm, only about 5.5” was insertable before she’d say “ow”. This is very strange because as I’ve said, I was certain that most of my actual meatstick was going down the rabbit hole.
I do have a theory that because my dick is innately curved and nowhere near as bendable as the jelly when hard, that more ‘apparant’ length will go in, but just have the effect of stressing the walls horizontally rather than actually going in to the measureable depth… yet another reason that curves kickass :)
The funny thing is that in doggy style, she can take much less, perhaps because in that position, my dickhead is pointed directly into her cervix?
I can draw a diagram for those curious yet confused people… ;)
As far as the dumb people, thal, it is a two way street as has been previously discussed here. It is as much a girl’s responsibility to be fit and tight for her guy, if not more so, than the guy to for example, practise PE. (Because we all know how much more difficult it is for us to make any significant changes!) Only the most ignorant/selfish of cows would complain about her guy while simultaneously sitting on her can doing squat all about it herself either.
In terms of PE, I would estimate conservatively that the classic 8” length is probably as far as you would want to go for functionality issues. If you land up with a cavernous girlfriend then you can always come back to it later to fill out that last inch or two(!!!). Me, I am shooting exclusively for girth. If I could take an inch (or even two!) off my length and add it to girth, even at a reduced ratio, I would in a heartbeat since the last few inches at my base have never before and will likely never in the future see the insides of her pussy :(