I HAVE DRIVEN ON THE ICE WITH MY WELDED DIFFERENTIAL, in fact, it was a week or 2 ago. it was fun, but yeah, a little squirly. the thing is, wheelbase helps, the more you have with a welded or spooled rear end, the less likely it is that you will have the rear end passing up the front end, especially if you also have good snow tires, i run 38" swampers, not the best for anything other than mud or rocks. our wheelbase is actually pretty long for small suv's even though our overall length is short. so, it helps, but, yeah, i'd imagine no matter what precautions you take, if you are fully locked-up in the rear, you can lose lateral traction on ice, it's just the nature of the ice, though, not the differential. it's my opinion that ice should not be driven on if at all possible anyway, but, hey, i'm not the company bigwig that can tell you not to come to work that day.

so then let me rephrase:

if you live south of say, Nebraska, welded is good for you, if you live north of Oklahoma, selectable is prolly better, but it all depends on when and where you drive, too.