Well, I think it is pretty likely that if you go about it sensibly, take your time, and stick with it, you will be able to gain an inch of length and 1/2 inch of girth, perhaps more. That would give you a unit that the vast majority of women would find plenty big enough, if not huge. If you are regularly having sex you will probably know if you are getting uncomfortably large for the woman you are with. But beware, since gains are gradual, your regular lover may adapt to you and have no difficulty whereas a new lover might possibly find you too big.
I do think that women in general are excited by large cocks, as long as they are not ridiculously big. But if you are going to be in a long-term relationship with a woman, what may be very exciting to her at first, is going to become more common place over time. A really long penis will prevent you from entering a smaller woman fully which will limit close pelvic contact and will require you to exercise more restraint than you might like. It will make quickies much more problematical. Some women will be sore enough after sex that they don’t want you to come around again for 3 or 4 days.
I am around 5.6 inches average girth and around 6 inches at the base. I have had quite a few a women complain of a lot of jaw fatigue when giving me head and I have had to put up with a fair number of tooth scrapes. I have heard the same from other guys around the same girth.