I think you will be fine either way but since you have a 10ft rod the bg5 may balance it out better.
I would bring the rod down to the fly shop and they should let you put them on your rod and get the one you feel balances out the rod. Having a balanced set up helps fight fatgiue as the day goes on.
Backing should not be a problem with either one. I think you would have plenty with the 4 or 5.