Mel,
The Kauai 6-5-0 is the mountain model that utilizes the new 650b wheel size platform.
The wheel is positioned between the standard 26" and the 29er in diameter.
This new size allows for greater rolling momentum and trail smoothing due to the larger ground contact patch than a standard 26, while reducing the slower acceleration and design compromises for smaller folk that the 29er requires.
The use of the 650b wheel size allows for more traditional geometry, keeping a quick front center and excellent climbing traction due to shorter chainstays and larger tire to ground contact for traction.
It really is positioned to be a well balanced design that has alleviated the compromises that the other sizes have suffered from.
I'm scheduled to build quite a few in the next month, including one with S&S couplers for travel...should be cool.
Cheers,
rody