I go with 23s all winter and a front brake. Only fell victim once last year and that was in fresh deep snowfall that completely hid all reference to where the streetcar tracks were. That they were also iced over (unused streetcar tracks on Richmond W) helped quite a lot as it happened in slow moving gridlock and i was able to slide along while gaining my footing at the same time thereby keeping the car behind me behind me til I could step off to the right with my bike. braking had nothing to do with that one, nothing could prevent a lil spill. cold-snapped my fender though, it was too brittle from the chill when it slapped the ground.

If your line is true and you aren't yanking on them front brakes work just fine on ice. Momentum will save your ass.