Why not take both dirt and road tires and enjoy the best of both worlds. For a five day ride depending where you are going you should bring an extra tire anyhow so you would be taking two extras instead of one.
My wife and I are going to be riding around the Klamath Basin in early September, self supported. There will be 80 plus miles on the old OC&E railroad bed and some National Forest dirt roads and trails, and a lot of paved roads including Crater Lake (if the snow ever melts).
For my wife's MTB she will have 1 5/8 x 26 dirt tires and a 1" Hutchinson Top Slick 2 front and 1 1/4" Panaracer T Serve rear street tires. I will be running a very similar tire set up on my cyclocross bike with 700mm rims.
After a week of riding, hiking, and birding she will take the Amtrak back to Portland and I will follow the Klamath River with lots of side trips on National Forest roads using my dirt tires and eventually end up on the Pacific Coast and head down Highways 101 and 1 to Moro Bay, California with street tires. And if I see a dirt or gravel road that looks like it needs exploring it takes only a few minutes to change tires for the adventure.
There are several inner tubes that can span narrow to wide tires so you only need one extra tube or how ever many extra tubes you normally carry.
It was to such a land I rode.
This message was edited by WesternFlyer on 8-12-08 @ 4:58 PM