What is your commute like? Many hills or planning on running hills?
I would go with 4.56. In town mileage will be reasonable, maybe better than current. RPM at higher speeds will increase a small amount, nothing the 4.0 can't handle.
You may want to step up to 33's or larger at some point, which the 4.56 will help.
I got my 4.10 geared axles for a really good deal, that is why I ran them with 31's, and now 32's since JK wheel upgrade.
It's definitely better than 31+ with stock gears.