Ok, I have Schwalbe Marathon winter on my winter bike. I've found that -

1. They are the most efficient studded tires I've tried, the Nokian 240's seem to add noticeably more rolling resistance, the Nokian Extreme's feel like riding a tractor.
2. To a certain point you can get more grip by putting less pressure in them, but only to a certain point.
3. As everyone else said, fantastic on ice, and good on certain types of snow like fresh snow where the tire can cut through the snow to pavement. I've found them pretty decent on smooth hard packed snow as well (like on the MUP where it gets packed down into practically ice).
4. I did ride last year on some hardened but rutty and pitted snow on the MUP. It was a real PITA, and a ton of work, but I never fell down or felt like I was going to (though it took a lot of work to stay upright).
5. It did fall down once, though, on the street. The city hadn't really plowed it at all, and it was this weird mix of semi-packed snow, loose snow...it was just a big pile of snow on the street that had sorta been driven over before. It wasn't a big deal for me because it was a side street and there was no other traffic, and the very snow that caused me to fall cushioned my fall - it was like falling over while downhill skiing, no big deal. However, might have been different had their been traffic obviously. But...I'm just saying - I really felt like I would need a *much* gripper tire to stay upright in that situation. I did not try it, but I'm not sure a Nokian w106 would have made any difference at all. Maybe a 240 would have done it, I'm sure a Nokian Extreme would have helped.
6. But basically - any tire wide enough to make a big difference would have also been *significantly* slower the rest of the time. Actually, a lot of people even keep 2 winter bikes, one with the fat studded tire for that 10% of the time that you need it, and one with the skinny tires for the other 90% of the time when you don't want to lose a fourth or a third of your speed to the tires.