The steering angle comes from the CV. Even if a stock CV can turn 30 degrees, it may not be strong at 30 degrees so running hard at full lock is not advisable, especially when backing up. A wider axle can allow for more steering angle if you are already limited by the tires rubbing on your leafs or whatever, but it isn't part of the axle's design that makes it steer more.
I am having Diamond build me a housing with custom diff offset (moving the diff to the passenger side about an inch for pinion to oil pan clearance) so I can't use off the shelf inner shafts anyway. Brain will cut me a custom set of inner axles and I will use new RCV birfields at the ends.
The gearing change is noticeable, but the 3RZ really doesn't care.