I keep seeing this factoid show up in response to length issues and I'd like to explain why length is still important.
If the guy has a 4" penis, during thrusting the woman will feel on the in-stroke 1",2",3", 4" and on the out-stroke 4", 3",2", 1" of vaginal sensation.
If the guy has an 8" penis, during thrusting the woman will feel on the in-stroke 1",2",3",4",4",4",4",4" and on the out-stroke 4",4",4",4",4",3",2",1" of vaginal sensation.
A longer penis will stimulate those 4'' for more duration than a shorter penis can during thrusting.
This is in addition to the pleasurable sensations from pressure around or on the cervix which is entirely dependant on length.