Does penis size really matter?

Ok, this is a serious question that is hard to get a real genuine answer. I am married, and even though I am not small, I don't consider myself well endowed either. According to my wife, she says that I am perfectly fine and that she would not want any bigger. But, I know that I really cannot trust her opinion, simply because of her not wanting to hurt my feelings...So, does this really matter? What size is "perfect" for most? Is the average 5 1/2"-6" length acceptable? Please enlighten me..