My understanding (which includes a little research into the subject) is that the average erect penis is between 5 and 7" long. (LOL - I always like to be above average!)
I definitely think that it entirely depends on the woman (or man) as to what size they prefer. Nicky definitely prefers ones on the larger end of the scale (though that doesn't mean she won't play with people smaller than that.) But on the other hand, I have been with a couple of women who found I was uncomfortably or even painfully big.
Vive le difference - that's what I say!
Russell