from my experience, women, excluding size queens, are a lot less concerned and a lot less knowledgeable about "big" dicks and what is considered big, you have to remember they don't have the privilege of going in men's locker rooms, and most of the dicks they have seen, especially erect, are those of their partners. especially if you are in an emotional relationship, dick size is not that big of an issue with (most) women, unless it is abnormally big or small..... they'll usually only say something about how big it is if it hurts. that being said, if you tell her you get off on hearing how big your cock feels to her, she will probably abide, and give you the assurance you need.... depending on how much she likes talking dirty. hope this helps.
again this is from MY personal experiences, if anyone feels differently or has had different experiences feel free to leave your two cents.