Ksyrium's are great. Stiff, light, very responsive, durable, and did I say stiff? If there was one drawback it would be that the ride may be a tad more harsh than an equivalent carbon set, but they're not ridiculous. I've abused mine over many thousands of miles with only a very minor truing needed once for the back.

BTW....mine are the SL's (or whatever they call the lightest set these days) with zircal spokes, which is the pair I'd recommend.