This is always difficult. I have never measured a man I have been with, and I haven't been with a man in a very long time. I never use toys and never have, and I am able to squeeze my one index finger tight enough that it makes quite a sound when i pull it out. I am sure my finger is not 5 inches in girth- lol- but it is not the friction of the vagina that makes me cum anyway, it is the combination of that and clitoral stimulation. So I would think 5 inches girth is more than well equipped to feel tight and full inside, unless the woman is very very loose.
reminds me of a joke-
"open wide" my husband cried. I really did, he fell inside!! (Wasnt me, havent had a husband lol)