When I ordered my new one last year, upgrading from the gen2, I figured I could take the 4.75. It was friggin massive, so I sold it and got the 3.75. Perfect size for me.
Granted, I don't use it for play, but imagine walking around with a 5.5 hose in your pants all day. The silicone is pretty rigid so it will look like a semi at the very least. Maybe if you expect to have a lot of sex, it'd be ok, but if your main goal is packing and peeing, I'd advise to go with a smaller, if not the smallest model.
Also remember that the average size of a flaccid penis is about 3 inches.
For reference, I'm 6'2"