There are simply too many options in good tires now to buy a bike with less clearance than 50mm tires and no real reason to ride less than 40mm tires. My opinion is that if might be riding off pavement, I want 50mm tires....at least.
OP, if you are looking for a bike, find a Surly dealer and test ride a Troll, Ogre or Karate Monkey. Any of those would be fantastic for the riding you are describing and you would have maximum versatility in tire width.
Last edited by corwin1968; 01-30-16 at 09:43 PM.