I hate to be cliche, but what about how to use it? Women's vaginal canals have not lengthened as men's penises have grown you know.
A few hundreds year ago the average was about an inch shorter thsan todays average (5 inches instead of 6 inches for the average caucasian) and that was considered a good fit with your lady friend. A longer penis has more chance of hitting her cervix, and if there's one thing you absolutely do not want to do during sex, it's hit her there. Flailing, kicking, throwing you out of bed and probably not letting you near her for the rest of the night will follow depending on how hard you thrust.
Also, the key is width. Remember that the cluster of nerves you're looking to stimulate is only an inch or so inside, and located on the top. It won't matter how long you are if you aren't thick enough to be hitting that spot.
Curious as to whether any ladies are reading this, because I find that usually they give a better idea about what women actually want from a penis, what with being women themselves and all.