I will recommend the Surly LHT for your application, particularly if you fit a 54cm frame (which is what I have) or smaller. At 54cm and below they are designed for 26" wheels.

I have 26", 36 spoke Velocity Aeroheat rims on mine and once hit a bridge joint at the bottom of a hill at speed with enough force to break the belts on the rear Continental Travel Contact tire. The rim was okay.

The Travel Contacts that I use come in 26" x 1.75" and are smooth on the highway (cause they have a smooth center to contact hard tarmac) and are great in loose gravel because they have knobbies on the side. They are heavy, though. I also use SKS fenders and there is no clearance problem (26" remember).

All-in-all, the 26"-wheeled LHT brings to mind the tough little ponies one sees on the plains of western China.

BTW, I think you should edit your original comments about the 520 being flimsy...It just ain't so.