I've been using my road bike (all aluminum except for the fork, so not exactly built for the weight) this fall for touring and it's been working beautifully. Thanks to a nicely timed run-in with a car I got a beautiful new rear wheel made specifically for touring which makes me a little more confident with loading up the bike. Maybe try that if you're really concerned? The top of the line Mavic touring rims are only about $75 or so, and I got a fully built wheel with a tiagara hub for about $200 (in extremely overpriced Toronto).