It is all on who the woman is really, some women like to be fisted, others have to really work themselves up for a while just to push two fingers in (like my girlfriend). The average penis should feel perfect with the average vagina. Looking at statistics, it looks like anything under 4 inches is thin and no longer in the "normal" range. A perfect average is between 4.5 and 5 inches, where as low average is probably 4 to 4.49 inches and high average is more like 5.1 to 5.25 inches from all the reading I have done. Plenty of testimonials I have read from the womans perspective considered a 5 inch girth thick and no longer average. That said, no woman wants something so big it hurts, but some still don't even like the "thick" feeling, claiming it makes sex more difficult and makes her feel crammed, some women actually prefer the feeling of a thinner penis, I have heard it described as a "gentle massage" inside her vagina. The average woman is most likely going to prefer an average girth. I am not saying this because I have an average girth of 4.5 inches, it is just the direction everything points towards if you get enough opinions, and it also just makes perfect sense. If you are feel you are too thin OR too thick, fear not, if you fall in love with the right woman she is not going to care, even if you are not her perfect size, the size of your penis will not put a halt to a relationship with a foundation of strong emotions.
That is my two cents on the whole girth thing. Sounds awfully conservative for someone who is aiming to gain .25 inches in girth. I know my girlfriend would probably never tell the difference between 4.5 and 4.75 inches in girth, but I am doing it for myself, I aim to be the perfect average.