I'd take a limited slip or a GM locking dif over an open dif any day of the week. It's what gets you going at low speeds that matters most.
At highway speeds on super slippery roads it's time for 4WD drive and avoiding mishaps has more to do with tires and driver control than what type of rear end you have. I've been on roads that were so slick (Palmer to Anchorage) I didn't go faster than 40MPH in 4WD and even going that fast had an extreme pucker factor. The people that drove faster were ditch diving in front of me, to the side me, and behind me. It was insane.
True traction control systems are superior to any standard 4wd system at both low and high speeds. Even FWD is better at keeping you out of the ditch vs 4WD at highway speeds.
