Length isn't that big of a deal. Depending on how the woman is built . . . some women can handle 7, 8 and some can handle only 4-6. I think width is more important. That said, neither length or width will matter, if you don't know what the hell you are doing.
If man is small or average, he can make up for the lack of inches by pleasing his woman in other ways. If he is on top of his game with the use of his tongue, fingers, hands, kisses, hell even the look in his eyes, she won't give a damn about his size.