I realize this thread is 7 months old, but I just wanted to share that the 2015 Trek Cali SLX uses Trek's smart sizing. Which means the 13.5" and 15.5" frames have 27.5" wheels and the 17" and 18.5" have the 29ers.

Curious which bike you ended up going with original poster? and what size did you end up with if you got the Cali?