Actually, historically, throughout Europe, bigger penises were actually considered beastly, or more comical. Other than that, there was really no focus on penis size historically, since most places were prude, or if they weren't, their food wasn't healthy enough to make very much differences in sizes. Just like, historically, most people were short, but all the same shortness by region.
Also, a penis too big damages the cervix, and prevents a women from getting pregnant. So the best penis is just long enough to be close to it without hitting to damage it, genetically speaking I mean.
If anything, how far/hard a male shoots his load probably has more of an impact on pregnancy than size.