It depends a lot on how you're touring. Hours/Miles per day? Days?

I put some Michelin Protek Max (32mm) tires on my Hybrid conversion. They're OK tires. A couple of thousand miles, and I don't think I've had a flat yet.

But, the added rolling resistance really beat me up with my last Eugene to Portland (and back) trip. 130 to 150 miles each way. My next trip will have to be on 23 or 25mm tires.

I'm working on my next "touring" bike build... hopefully. I have Surly ExtraTerrestrial 29 x 2.5" (63mm?) tires planned for it. It will take me a while to get it going, but hopefully it will be ready sometime this year. But, the bike will have a very specific purpose, of rough gravel touring.