You'll be fine with the 25s fixed. I ran 23s all last winter (also 5min from downtown) with only a few wrecks. Fixed is better for control on the ice, so that's the direction I'd go. It's also better not to use the brakes on ice.

I think the studded tires are really only usefull for riding on the lakes - most of the roads here are plowed/salted so quick that the studs aren't really neccessary. I'd also worry about riding anything with suspension - what happens when it gets really cold and all those parts freeze?

Couldn't you just take the fixed wheel off of your track bike, and put it on the Surly? Seems like that might be the best option. Then you could run the cyclocross tires, even though they do throw a lot more snow up, and create a lot more drag when you have to ride through any deep snow...

I might think of other options, but that seems the best right now.