You can cheat the walkway in a walk-in closet a bit if the walkway runs between shelves or rods(3"-4"). This works OK because the open spaces around and above clothes and shelves creates the illusion of spaciousness, which is why it doesn't work so well when one side is a solid wall.
So, 4' is too small, and 5' is a bit inefficient. A 5' closet will get you hanging clothes on one side, while a 5'8"-5'10" closet will give you shelves on one side and hanging clothes on the other and a 6'8"-6'10 closet will get you hanging clothes on both sides.
In your room, I would probably try to 5'10 and would not do reach in closets, but I like wall space. Your bedroom will still be large enough and you will get shelving in the closet for shoe shelves or anything else. I assure you that you will not have any trouble finding a good use for closet shelves.
Here is a quick mock up...
Q