We are a 300 lb tandem team, but have also given up on the Velocity Dyad rims. I'm much happier with the Mavic A719s that I replaced them with. The Dyads were not great at staying true, but the bigger issue was that two separate front rims both developed bulges in the rim after long, steep descents with lots of rim braking. The rim actually became slightly wider at one point, causing the front brake power to give a pulsing feel. I've had no such problems when using Mavic A719 rims (36 hole on the front and 40 hole on the rear).
As for average team weight,
Wikipedia claims an average male in the US weighs 190 lbs, and an average female 165 lbs, making 355 lbs total. The total for the average male+female in Germany is 25 lbs less, and there are other European countries where I'm sure this would be reduced by a further 10-20 lbs.