With the stock bumper, you will rub with even those 305 Duratracs 34" AND 4.5" BS, when your off road and fully articulated.

Something to be mindful of. If your going that way, look into Snarf's Stock bumper mod where he cut the ends off.

Not a bad idea to go for a little less backspace.

Ive ever heard someone say... I wish i had more backspace. (4.5+)

Ive defiantly seen rubbing and tire damage and people saying they WISH they had less backspace.