This is an interesting topic... I have an average sized john... My gf complimented my size several times in comparison to her previous guys, but overall she doesn't care for size at all. It doesn't make her feel any better if I go further in. In fact, she likes it near the entrance... So go figure.
Sure, we can argue all day that once a certain girl tries a bigger sausage, she'll finally know what she's been missing. But all my g/f's were perfectly satisfied with my average shlong and some were actually feeling pain or discomfort when I went deep. I cant imagine them enjoying sex if someone went deeper.
I think this discovery is much more important for those with deformed, sick or otherwise damaged dongs. For example, there was a Russian movie I saw about the guy working as border patrol guard. He captured a truck full of drugs trying to cross the border. Those guys went to jail and drugs were seized.
So the bad guys got back at him. They caught him, brought him to the top of a cliff, cut off his mandingo, and threw him down in a river to die.
He survived. Swam back to shore and passed out. The vultures ate away at his legs before he woke up. He crawled back to town, to his beautiful wife at home who he could never make love to again. Wife didn't leave him. She cared for him and worked, while he went around town in a wheelchair begging for money for many years...
Long story short, eventually, in China, the doctors performed an experimental surgery where they transplanted a new(err.. used?) Mr. Happy to this guy. The doc did a miracle, and the guy was actually able to have kids with his wife and live happily ever after!
The crazy part is that this is a true story, with some exaggeration of course. There was actually a soldier in Russia who had all this happen to him.