I'm only 230 but I run Zipp 404's on my tandem and our weight there is around 350. My race team's mechanic had extensive conversations with an engineer at Zipp about our application and he said that for our weight the 404/505 rim depth was optimum. We wanted to go with the 808 but he was concerned with the spoke angle. He thought that might lead to premature spoke failure. With the 404's I've done two 3000 mile races and the associated training rides (probably around 10,000miles) without a spoke failure. I did break a rim when I hit a pothole at 50+mph. Take that for what it's worth. Good luck with whatever you go with.