I would be interested to see this answer.
My thought, reinforced by what I have read is that women do not cheat for physical reasons, they cheat because they are being shortchanged emotionally. I think this site would love the notion that females would always want a bigger dick but thats baloney. Once she had made her choice, and dick size is a not that big a deal (pun intended) for most women in choosing a life partner, they roam because they are not being supported emotionally, they are not valued as a partner anymore.
No matter what you read on this site, remember there are only a few women here so its a very skewed sample, go read women's magazines to get the real scoop. They want to feel emotionally connected and supported by their partner. (they also want a LOT more oral sex but thats a diff topic). Most women are not gonna blow up a LTR where they are supported and valued because of a physical attraction to another.