The 7900's are an evolution of the WH-7850-C24...a very highly regarded wheel.
Personally, I would look at the Shimano RS80. It uses the same wheel and spokes as all of the C24 wheels, but uses Ultegra hubs instead of Dura-Ace. Result: Way cheaper and only slightly heavier. ribblecycles.co.uk has them in stock for ~$445 and you could save your Performance points for something else.
Some links of interest:
http://www.youtube.com/watch?v=nPW41cnuy30
http://www.youtube.com/watch?v=qOM9UMEg8HA
Bob