As a gentlemen, I've always tried to think that the ladies consider penis size the way I consider breast size.
Despite popular culture claiming that "bigger is always better," most gentlemen would agree that there is a too large and there is a too small. Further, some gentlemen prefer double D's, and some like Bs or smaller. Some don't care what size so long as they're natural. But at the end of the day, a preferred size is really only "important" to a vast minority. While most guys notice and do have some preference, it's not on any levels important unless its at one end of the far extremes (I'm talking the 1% or less on each side), unhygenic (take a shower woman!), or unless there is something unnatural that turns a guy off on them (i.e., pierced, tat'ed), and even then some people love that kind of stuff. Instead if a girl has the perfect breasts, that's just a bonus and something the guy will love, but generally is not something the guy would get hung up about.
In my experience, most ladies have similar considerations about a fella's tool. So long as its not at one end of the severe extremes, clean, and falls within their tattoo/piercing requirements (and (un)circumcised etc.), most don't care but would consider it a bonus if the tool was ideal.