Hi TigerMom.

I think I remember you saying you were having some trouble with switchbacks, is that right? If so a 27.5 would be a better choice over a 29er for the tighter turning radius and also your height. The Niner has a effective top tube length that is about 2.5 cm longer and a wheelbase that is 3 cm longer. The head tube angle on the two bikes is the same so the Niner will feel more stable at high speeds, but will be less responsive turning and the reach will be farther.

Are you bent on carbon? Are there any other models you've considered?

Hope that helps.