I can go to 45mm with my roadbike (rivendell sam hillborne), but it isn't a racebike and I'm not pretending it is. I use 38s on it now. You could look for a touring bike like the Jamis Aurora, but a cyclocross would work too and would probably be a little bit better for dirt. The Jamis will be more stable under load and the cyclocross more racey in geometry. Cantis or V-brakes for wide tires help when you get a flat. I think touring on a racebike would truly suck.
Really? Why do you think that? Is it because of the position you're in on a road bike? I thought without panniers and a backrack it might be OK but...