I was considering these for my 2004 5900. Little heavier than K's but I have always liked Shimano hubs. Any thoughts. Any professional reviews on these wheels anywhere?

Initial response, based on a 25-mile ride with intervals yesterday, and a 60-mile team training ride today. (My bases for comparison are my "normal" 32-spoke Open Pro training wheels, and AC350 race wheels.) The Shimanos feel very fast and stiff. (Take that in the context of a 140lb rider.) Definitely feel faster than the OPs, probably similar to the ACs (I'm not super-sensitive) but stiffer. To be honest, they don't feel heavier than the ACs, although by spec they are; perhaps the hub-mounted nipples & reduced rotating weight account for the similarity. They are not quite as compliant, as you would expect from any reduced-spoke-count wheels (higher spoke tensions) and the slightly deeper rim section. I like them a lot. Enough that I will use the ACs for the early season crits, so that if anything gets wrecked, it isn't the new Shimanos.

Shimano Dura Ace wheels are awesome. If you're interested, i'll elaborate.

Please elaborate.

I bought a pair of WH-7800s for 500$ from Totalcycling but have yet to actually ride them (I am waiting to put them on a new Colnago frame I ordered). Currently, I ride Ksyrium SSCs and they have been very reliable and nice wheels. No major complaints with the Ksyriums but I decided to go with the WH7800s for three reasons: price, aerodynamics and aesthetics. After doing a little investigating it looks like the WH7800s weigh about the same as the standard SSC SLs (ok, within 30-50 grams or so if I remember correctly). However, I have always thought the Ksyriums were very non-aero. They have sharp box shaped rims and the spokes/nipples are very large at the rim. In crosswinds the Ksyriums always moved quite a bit too. The WH7800s have a lower spoke count and look a lot cleaner with regards to aerodynamics and I imagine they are much better in crosswinds. I don't know if this is well known but it looks like the WH7800s are built up with the very nice Sapim CXray spokes (at least they have SAP stamped on the spoke and look just like Sapims).

Anyway, I can't wait to ride the. Until then I would like to live vicariously through your description of how they ride.
Cheers

Yes, SAP is Sapim's stamp. My LBS has the carbon rimmed versions in stock. Neat looking wheels, very subdued spun/unidirectional carbon finish or construction for function and not appearance.