speedster on 5/17/2012 6:35:31 PM:
I've done a large section of the C&O on a 32, no flats and no issues.
Your thinking of using the thinnest tire (within reason) seems right to me. Less rolling resistance, which consumes less energy by the rider while pedalling. Over a sustained distance, the savings in energy exerted is substantial. Your average speed will be higher and you'll presumably finish earlier (which near the end of your trek, the finish will seem like it can't come soon enough!).