In reply to jethro kiernan: RS81 are the same rims as the DA C24s, but on Ultegra hubs, I think - so I guess it comes down to price.
I run Racing Zeros on my best bike and Racing Threes on my winter bike, but mainly because they're "tubeless ready" and the Shimano wheels needed special valves etc last time I was changing. If Wiggle are doing a special deal I got my Zeros for £599 - I have a spare set sat in my office because the price was so good!
Had DA C24s before these though, and they are bloody awesome wheels.