My commute was 25 miles each way, 1400 feet (426m) of ascent each way, with no transit option. Last winter, a surprise blizzard rolled in during the week. My ride home took me 2.5 hours, rather than my usual 1:40, but I managed to stay upright the whole ride despite riding on slicks. Fixies and foul weather, better together!
My fixie has brakes, so for me, less strength than JRA. On my snowy ride, stopping the cranks took no effort at all. But keeping the wheels turning acts as a kind of traction control: if the cranks suddenly require less effort, that tells me there’s an icy patch under the snow and I need to be extra careful. That surprise blizzard was my very first snow commute where I didn’t fall. It was also my first time doing a snow ride on my fixie. Not getting a bunch of speed in the first place helps a bunch.
Now, if you’re asking about riding in dry conditions, let 'er rip. I can spin comfortably up to 135 RPM, and have gone up to ~150 RPM with A LOT of pucker. Usually, when descents got to 135, I would take my feet out of the pedals, which is its own kind of bad idea.