Well just under 16 miles on the new Marathon Winters, average speed just under 13mph. Was taking it easy and this included some MOD roads so little regular traffic and no gritting etc. The tyres did what I expected on ice etc and were far better than I expected on tarmac. Ran them at 75psi and they felt as comfortable, and no slower than, the M+'s in 35mm that they replaced. Passed a guy wheelspinning a MTB going uphill, that was the only way I realised it was ice, I hadn't noticed. Only hairy moment was on the MOD roads as it was turning to slush and breaking up. I thought I was going down, my frantic overcompensation brought me back too far. So I slalomed for about 40 yards, I was genuinely surprised the tyres gripped at the angles they were leant over. Proceeded more carefully and they really don't like slush, squirmed a lot(think loose gravel feeling), but very controllable, though still tiring and needing focus. But no way would my normal tyres have kept me up, even serious knobblies might have struggled for grip.
Verdict - my rough calcs indicate that I'll be able to tool along averaging about 14.5-15mph in regular conditions. They will grip on ice and perform heroics keeping me up on looser stuff. There's a bit of noise but not enough to annoy me. Unless they fall apart really quickly I see no reason not to run them the entire Winter. But can understand that if you're going from a lighter faster tyre then it may be too big a penalty to consider. Obviously clearance is an issue for some bikes as well.