B/c a lot of girls I know have seen or been with a person with a penis size of 9 or bigger. I even know a girl who has been with multiple 9+ guys so I would say if anything to do it for yourself or to have any chick you get with brag about you.
Penises 9” or longer are probably as rare as something like 1 in 1,000, so that is unlikely. As has been discussed here many times in the past, women seem to pretty consistently overestimate penis length by an inch or two, perhaps due to a combination of the angles from which they look at penises and poor size judgement. It would probably be relatively rare, that a woman had actually even seen a penis as large as 8”.