Two things to be aware of, the skinny Race Kings don't have the grip of the 2.2 's and the UST Race Kings aren't Black Chili rubber, so they don't have the grip of the Supersonic/WC Black Chili version.
From the Conti UK website...
Available in two widths of 2.0" & 2.2", large volume casing combined with a low profile tread pattern and Black Chili compound are just what ensures a head start on fast paced technical world cup tracks and marathon trails.
ProTection and wire/fold variants are also available (non Black Chili), along with 29" and UST versions which will be available in 2009.
From the German Conti website... OK it's in German, but you can tell that only one of the series is listed with Black Chili rubber.
* Race King Supersonic: 3 Lagen/ 180tpi/ faltbar/ Black Chili Compound
* Race King ProTection: 3 Lagen/ 180tpi/ faltbar
* Race King UST-Tubeless: 3 Lagen/ 330tpi/ faltbar
* Race King: 3 Lagen/ 84 tpi/ faltbar und Draht
* Race King 29inch: 3 Lagen/ 180tpi/ faltbar