In the last nine years I’ve almost always toured 28f and 32r with a number of different brands and models. I've no intention of changing. My current choice is Conti 4-Seasons. They’re light, smooth as silk to ride on, unbelievable traction wet or dry and best puncture protection of any tire in that weight category that I’ve toured with. They’er not cheap.

You say your tour is approx. 20% dirt. Is that going to be long stretches of dirt, say most of a day, or going from sealed surface to dirt on and off all day long? When it’s the former I take a separate set of dirt tires, 40mm, to switch as needed. If it’s continually on and off dirt to sealed I’d consider some 35mm cyclocross tires designed for fast rolling on compacted dirt. Run them inflated high for the sealed and let some air out for the dirt. (Bring a good pump.) Schwalbe SV18 are excellent tubes for skinny to fat tire switches, as they are rated 28-44mm.