I've tried studded tires from 2" wide down to the 30 mm A10s (officially 32 mm). The advantage of a thin tire is that it will cut through snow and slush more readily than a wider tire. This can be both good and bad. The firmer the snow or slush, the less desirable this is. A wider tire will float easier and gives a better ride on rough and uneven surfaces. Thinner tires will typically slow you down less when conditions allow you to move at a quicker pace.

Though you put it in the "thin" range, I consider 40 mm to be about medium width and the w240s at 40 mm for me represent the best compromise, -though different tires will be better in different conditions.