Curious study. I personally only have my self as a test subject, so it's quite subjective, however I use the foreskin quite a bit for stimulation, not really as an erogenous zone, more of a way to slide it in, it also helps prevent lubricants from drying up, since without at least spit it just hurts. It's REALLY sensitive under there and fucking hurts when rubbed by just about anything else, if I didn't have foreskin, it would have to become significantly more numb before I could rejoin society. Actual sex might not be as affected, but masturbation as I know it would cease to be.