4WD Speed

I wouldn't worry too much ... we regularly run for 10 - 15 miles in Low ratio when green laning.
I always drop into 4L and use 1st / 2nd when fording water or driving through mud.
In snow, I quite frequently mess about with 4wd and 4wd, just to see how far I can get, but have driven 50 plus miles in snow in 4wd. Its just that extra Grip.

Indeed, I have spent all day and done over 100 miles in 4wd switching between High and Low where needed, but keeping the hubs engaged.

At the end of the day its what its there for. Just respect that the handling characteristics at speed may also change

Unless your doing Lock to lock turning, your not going to wind up your transmission.. All your going to do is increase your fuel useage, add extra wear and tear to your low ratio's in the transfer box.

Ours is an auto so when switching to and from 4WD I've either been at a standstill and in neutral or no more than walking pace and with the throttle backed off and just applied enough pressure to let the lever slide into position easily, never forced. If it were an manual I'd dip the clutch to reduce any stresses.
Most we've been up to is mid 30s as if the conditions are bad enough to warrant 4WD then anything more isn't much of a priority. Does give a great sense of more control and ability in 4WD over this recently interesting winter and allows you to concentrate more on the hazards. The snow and ice didn't faze it one bit, absolutely love it!