Fyi, other posters mentioned this, but many studded tires are designed in such a way that inflating them to high pressure brings half or all of the studs off the ground. Schwalbe Marathon Winters have 4 rows of studs, at high pressure only the 2 center rows hit the ground. When you want more traction on ice let some air out of the tire and you get 4 rows of studs in contact with the ground. 45nrth Xerces tires have 2 rows of studs, at low pressure they don't contact the ground when going straight at all. The idea being that if you start slipping the tire starts to slide and catches the studs. Or you can let air out, and have both rows in contact with the ground if the weather changes while riding or on your way home.

Once I start seeing any ice on the road I always ride the bike with studded tires for the rest of the season. But, I do ride them at high pressure when the conditions are better, they're faster rolling that way.

Here in Minnesota I haven't seen any storms yet, last night I was riding my road bike with no studs - it's kinda funny, it's still noticeably slower when it's around freezing than it is when it's warm out. Something about the colder air being denser, grease in the hub getting the same way, and the rubber on the tires being less pliable or something.