- To begin with, bigger tires can run lower pressures. See PSI Rx.
- Studded snows are a bear to pedal anyway. The little bit added by lowering the pressure isn't noticeable when factored in with that, and with the added horsepower required to get through the darned snow anyway.
- The issue is control and traction. Lower pressures allow the tire to conform to the shapes of ice ruts and so on, so that they don't push the bike around, and so that you can maintain traction. In the absence of control and traction, you're walking anyway.
My four-seasons all conditions bike has a road triple (52/39/30). In the three seasons I run a 12-23 cassette it, and seldom use the granny. In the winter I run a 12-27 cassette on the same bike, and use the granny for many climbs. It's just a fact of life.
On the plus side, come spring, when you take the studs off or switch to your three-seasons bike, you'll fly on the flats and climb like a goat.
True story: My club's first ride of the season is a hilly one (Darned sadists!) It concludes with a long grinder. Last spring, after pedaling the darned studs all winter and cursing every mile, I took my Litespeed with a standard 53/39 double and 12-23 cassette on the ride. Not only did I pass everyone on that hill, I completely dusted a Cat 3 racer who ended up puking at the top. Not bad for an old guy on a standard double.