8 3/8" vs 4"
The 8 3/8" version kicks less, has more velocity, and throws less of the blast back at you. It is heavy and bulky though and much more of a man portable weapon than a handgun. For range use that would be fine, and it would fine as a primary hunting arm.
The 4" seems much lighter, even though it is probably only a 1 lb difference. I bought mine from CDNN for $799 (not sure if they still have them) and it came with a holster and cartridge carrier, which are actually somewhat practical as the firearm carries decently in it. Recoil is more with the full bore rounds, and it does throw out a big fireball and heat/concussion wave with them, but is plenty shootable. For a bear defense gun or a fun gun it would work well. I find myself shooting it more than the 8 3/8's as it is a bit more wild or fun to shoot.
You could always split the difference and go with a 6.5" model.