I have a set of shimano rs81 c35s. They are great for a stiff aero wheel. They feel stiffer than my 5 year old mavic ksyrium sl ssc. They are heavier but they don't feel like it. Most of the extra weigh is in the hubs and the steel freehub body.
I think they are the best wheel on the market right now if you are looking for a wheel that can be ridden everyday and still raced on without destroying your bank account.