This is your answer. I regularly ride on groomed ski trails, and ski the very same trails, and it depends upon snow firmness.

When it's firm enough that my 2.1 inch tires leave no rut, then I'm the fastest beast out there, no contest. I'll blow by skate skiers, classic skiers, and Pugsley riders every time.

When is soft enough that I sink in about 1-2 inches with the bike then everyone blows by me, Pugs, skate, and even a few classic skiers.

Softer than that, I don't take the bike onto the trail. But when I'm out skate skiing in it, Pugsley riders are left in the dust. Their floatation advantage seems to only extend over 1-3 inches of soft snow. After that, it's a skier's game.

I've only ever been passed by a classic skier once while I was skate skiing.