During my time at university, a friend of mine and his girlfriend were into swinging. He arranged most of their meetings through one of the many swinging websites on the net. Out of curiosity, I asked him if I could use his password to log into the site to see what kind of adverts were there.
Because this was a pay site (and quite expensive too), the people advertising were obviously serious, and were posting genuine adverts.
I did a quick check, and in just over 80% of the adverts, it was specified that the guy “should be VWE”, “should be VVVWE”, “should be at least 8 inches”, etc.
Obviously these are people looking for SEX, not RELATIONSHIPS. But it showed pretty conclusively that all things being equal, like Nman said, the statistical majority of women would indeed prefer a larger one.
Also, interesting to note that the ads all specified length, but not one of them specified a thick girth.