As we see in the above posts, tire width is a very personal thing, and everyone has their preferences for valid reasons.
I tend to agree with hueyhoolihan that:
too many variables to even begin making recommendations.. so i'll just relate an appropriate personal experience and the OP can extrapolate... or not.
I've never felt the need to use a tire wider than 32 mm for loaded touring. They are a good compromise between weight and comfort.
My wife and I have done a lot of loaded touring on 28 mm tires including a 3700 mile cross country tour. We encountered gravel, chip seal, Iowa frost cracks, and just some plain bad roads. However, we are light weights. My 155 pounds plus gear seldom puts more than 190 pounds on the bike, which allows me to get away with a narrower tire.
I tried running lower tire pressure in my front tire on a tour last summer, and had 2 pinch flats on the front wheel. I was using 32 mm Continental Gatorskins, and once I increased the tire pressure they were a great tire.
On another tour a couple of years ago part of our route took us on 400 miles of unsurfaced roads and trails, and over 500 miles of cobblestone roads. The 32 mm Schwalbe Marathons did well, even if they are on the heavy side.
