I am definitely not on the long side but sure I have some girth and, visually, at least to me, make it look shorter than it is but there are a few points which have to be underlined.
You can have 8"/20cm cock but if it doesn't get hard once you stuff that in it is not gonna hit anything...
Women seem to have two separate parameters to evaluate a cock, visual and tactile; I dated a much much younger than me girl, very attractive with a marble body and many men craving her attention, we didn't have sex before a few dates and when it did happen I had an undergoing flu I only later realised but I could tell something was wrong there and then as my performance was not even 50% of my usual. We broke up, we met again a couple years later and with that previous experience I was quite stressed and, again, it didn't work that well. Finally, like a year later, we met again and after a whole day in the sun on an open boat right before getting back to the harbour we started in the middle of the ocean but no visual contact of genital organs, once back and docked we both wanted to continue what we had to interrupt and to escape the surrounding crew's attention we slipped into the boat storage, enough to fit both but low, dark and hot. Long story short after pounding for like half an hour with she below and me on top I had to breathe and cool so I stood up and I was with my upper body off the deck and my lower inside the storage, the light eventually hit me, we were in almost total darkness inside, and then she came to me and said she had to apologise like "I really have to apologise, back then I thought you were small but..." My immediate thought was "what the hell, you can tell a cock size by watching it but not off the friction you have inside you???"
Visually I think it is matter of balance, body size/length/girth, you don't see many big guys/girls in porn, I mean body size, we all know that isn't it? In my case thickness is definitely here but it makes it look unbalanced with length, women side wise they all like it, they like the stretch both with vaginal and oral, anal, which I love, is little different cause not them all are into it and those who are won't easily accomodate girth, some are fine to play with a finger but my girth, not that I am Shane Diesel, won't encourage them to swap finger for cock...
Summary, girth does give pleasure, length, coupled with hardness, can give both pleasure and pain but visually I think matter of balance between the two with my ideal falling at 7.5x6, any recipe to gain that extra inch???