Re: full-time 4WD for off-road driving?
To go real slow over rocks you also need a low range (normally implemented in the transfer case), drive components that can handle the higher torque, and good ground clearance. Good articulation (suspension travel) also helps to keep the wheels in contact with the ground.
Lacking those things, it is hard to say whether locking in 4wd (driving the rear wheels at the same rpm as the front) would make much difference on rocky surfaces. It might be argued that driving all wheels will distribute the torque equally all around (strickly speaking only an open differential distributes torque equally), and reduce the chance of any one wheel spinning. But I suspect the border line between spinning a wheel while in 2wd and while in 4wd is narrow.
If it is not too steep, the automatic transmission allows me to crawl over rough spots (such as waterbars on decommissioned forest service roads). But for steeper stretches I need more power (not just more traction), and that means rpms in the 4000 range, which translates to ground speeds more like 10 or 20 mph. The manual is geared a bit lower, but does not have the torque multiplier, and requires feathering the clutch at low speeds.
In snow I think your best friend (besides proper tires) is 2nd gear. To avoid spinning (or either front or rear wheels) you want just enough torque to get you moving; too much breaks the wheels loose. The Element's automatic transmission does not downshift to 1st when in '2', limiting the torque you put on the ground.
paulj