I'm currently at 295lbs. I have several bikes with a range of wheels. I ride mainly for fun and for transportation. I've never "raced", but I like seeing how far we can push each other when riding with friends. I say this just so you know where I'm coming from.

For your situation, the best thing you could do is to get a 40 spoke wheelset built up around Phil Wood hubs. The extra spokes make a big difference in reliability and the tendency to stay true. A Phil cassette hub will set you back almost $400 bucks, but it sounds like you could swing it, based on what you've been riding. You also don't need to necessarily get a Phil hub, but I know that they make a 40 spoke hub. I think they could put a Campy freehub on there, but even if they couldn't, there are campy compatible cassettes available that have been milled to fit Shimano freehub bodies. As for the rim, I would recommend a Sun CR-18. They make them in 40 hole versions, they are double walled with eyelets, and will accommodate the 25-28 width tires that you should be riding on, and they are inexpensive. Mavic makes touring rims (don't know the current model number) that are of exceptional quality, but they will cost a bit more. Get those if you can swing it.

For your front wheel, any 36 spoke (or maybe even 32 spoke) wheel built with a strong rim (again CR-18's are really underrated) will work. Front wheel are built symmetrically and are inherently stronger.

For tires, I wouldn't recommend riding anything narrower than 700x25's. Anything smaller than that any you'll be giving yourself and your bike an unnecessary beating. Look for tires that can be inflated to 100+ psi. Do that and you will still have a fast tire. Panaracer Pasella's and Continental Ultra Gatorskins are two tires I've had good luck with in the 700x25-28 range. The Conti's in particular have been really great tires with good durability and a nice ride.

Some folks may think that a 40 spoke setup is overkill. I can say from experience that my 40 spoke Phil Wood wheels have done much better for me than my 32 spoke Campy Veloce wheels. Especially if you are going to be training on them, go for the big wheels. The weight difference is not something that those of us in the 300lbs neighborhood should worrying about. They will serve you well

Dave