Interesting to read this thread and to reflect on a few points that, in my mind anyway, are pretty clear facts.
Fact One - 26,ers are not better for downhill, uphill or flats. How many XC Or XCM competitors still ride them? And before anybody spews the nonsense about the pro's being sponsored, go and look at any big XCM event and see how many of the top 50% of the field are riding 26 inch wheels. I have witnessed in instant improvement in performance in many riders when upgrading to a 29'er, especially on long straights and technical up-hills. They are also great with the windy, technical stuff, but this does require a change in riding style. Also, worth reading about the Santa Cruz downhill riders who are using 29'ers for the World Cup this year because, even through they don't feel as fast, the times indicate that they are much faster.
Fact Two - Dropper posts, for a significant portion of mountain bikers (not towpath and blue route riders, but everyone else), offer a huge benefit. To be fair, no more than stopping and manually dropping your saddle before a steep technical section, but from a convenience and speed aspect, certainly they do.