Ok the thicker the man's penis is the more it's going to feel like the women's vagina ia stretching... much like it does when she has a baby... does a woman enjoy and thinks it feels good to have a thick baby stretching her vagina? And the average woman's vagina is only 3 1/2 to 4 inches long... it will stretch a LITTLE further... not that much though. There is an end to that vagina, ya know. Therefore do you think a woman likes haveing something that is 9 - 10 inches long shoved all the way in her??!! It's only going to go so far before it hits the woman's cervix ... normally shoving an object way longer than the vagina into a woman is going to make her uncomfortable to say the least. So unless the woman is into pain yes size does matter... we don't want them massive!
To the other extreme... if a woman can take just one of their fingers and insert it into their vagina rub that g-spot and give herself an orgasm do you think how small your penis is matters?
In my experience a man with a small penis can do a lot of orgasm producing for the woman as long as he knows how to use his equipment. Positions are the keys to it all. But that's a whole different story there. lol