FWIW, a couple of friends of mine do centuries around the Sierra all summer long on a tandem. They're both over 200 pounds, and they run really hard. They're using big tires, 700x37 Paselas, which help save the wheels, but they run 36-hole wheels on both ends. Haven't seen the bike in awhile, but I think the rims are Velocity Deep V's, which are pretty readily available. They also come in 40-hole, I think, with standard width and dish. If you can't find them locally, check
www.peterwhitecycles.com.