The OP's question is not completely offbase. From years of observation it is my belief that size queens make of 10% of all women. Latest studies have indicated that almost 50% of women have cheated on a bf or husband. I don't really have much else to base what I'm about to say on, but I believe 5% of size queens would cheat on their husband or bf if the guy's dick is bigger. Especially if their husband or bf isn't big. Of the other 90% of women who are not size queens, extra size is still of some interest to many of them. I don't think it is unreasonable to believe that a very small percentage of them would also cheat out of curiosity and/or desire. Perhaps only 5% of non size queens would cave in because of dick size, but I'm guessing a bit too much on the percentage now. At any rate, if so, 5% of size queens is 1 out of every 20 women, and 5% of non size queens is about 5 out of every 90 women, so that adds up to 6 out of every 110 women will cheat based on penis size.
I'm aware my numbers are possibly way off, but nevertheless, it's apparent enough that some women will cheat because of penis size. I personally knew a guy that had a small penis and his wife cheated on him with just an average penis because she wasn't getting any satisfaction. So those cases will also bump up the percentage a bit.