There's no "upper limit on penis size" but "'the most attractive penis size' appeared to fall outside the range used in the study..."

"... which was designed to capture 95% of the variability women would encounter. So although attractiveness beyond the 3 in. continued to increase in a linear fashion, it did so at a slower rate."

3 inches refers to incremental enlargements over a baseline that is never stated, so it's a tad hard to understand what this projected ideal actually is. The women in the study looked at "life-size video clips of computer-generated images of naked men who varied in height, body shape and flaccid penis size, but not in other qualities like facial attractiveness and hair."

Personally, I find computer-generated images very creepy, and I'd hate to be asked to take looking at naked CGI men with larger and larger penises seriously as a "science" experiment. Stuck down at the bottom of the article — which appears in Time magazine — is this: "height was as important as endowment in a male’s attractiveness, while wider shoulders and narrow hips was more important than both combined." In other words, after much obtuse blah blah blah about the importance of penis size and height, we're told that in fact wide shoulders and narrow hips are more important.

What a poorly written article!