Look at it this way; Sons usually inherit their fathers traits, right? From selective breeding, men with small dicks would have become extinct a long time ago if women were, infact, as obsessed with large dicks as everyone thinks they are.
From my personal research, how tight a woman is down there is directly proportionate to how fit she is though, so get out there and slay a few dragons but don't bother rescuing the princess, I'm 90% certain that it would be like throwing a sausage in a bus station. Your best bet is to go for a 7.5ish on the fit-o-meter.
Wow, that was a bloody nerdy post!