Given the advice and comments everyone has offered, I think I know what I'm going to do.

I have some 700x40 Kenda Klondikes from last year. They worked reasonable well, so I'll take off my front fender and run those at least to start. I may replace the front fender with mountain bike mud guards. I also may look into getting an even wider tire later on, since the front fender is off anyway.

Edit: Also, has anyone ridden Continental Nordic Spike tires?