I think she has been with two guys who were bigger than me. One of those was a once and done thing, she said he was huge and very very bad in bed. She remembered that a female friend who was recommending him to her said that his cock was like two coke cans stacked on top of one another, and, being young and adventurous herself, decided to give it a go. It sounded terrible though. The other guy was about 9 and was someone she saw for about a year, but she never got off with him.
My partner has only had extremes. The first guy she ever slept with she said was about 3 inches long. Then the next guy she hooked up with, after getting out of that relationship, was massive - the biggest she's ever seen (had to be huge to be bigger than 2 cans of soda), but they never got farther than her giving him a handjob. Needless to say, she was confused about penis size at that point in her life.
It's definitely given me some pause about my self-esteem but I think she appreciates me in bed and I am always open to learning and trying new things. I'm very focused on her and try to listen to what she needs and be attentive. We try to employ an "orgasm first rule" for her because she tends to get off in multiples if warmed up enough before sex, and she really enjoys that.