Weight of the bike makes a big difference in my experience, if you have like a 10 or more pound difference in bikes. My snow bike is geared a touch too high at 44x18 for going uphill all the way home in snow, but a lower gear would be murderous to spin all the way to work downhill in snow/sleet/wet - when there's not any snow, this bike is slow, heavy and sluggish compared to my road bike, and when there is snow, it's murderously slow and sluggish with a much smaller ratio than you're riding. My unsnow bike is a touch too high for the unsnow but very cold when commuting, but livable with the same ratio.

I think part of the "gear down for the winter" comes from an old training myth that you shouldn't ride a bigger gear than X in the winter because you've got to spin and keep up your aerobic fitness, suppleness and form. If it's terrain, gear down.