That would be my road bike... the 42 is so I can gain much more speed in the small ring vs having to go to the big ring in certain situations. I am also running a 54 big ring so it would not be good to have a 39.

12-27 is not much different up top then the 11-23 so I am not loosing much there

i.e. 23-21-19-17-16-15-14-13-12-11 vs
27-24-21-19-17-16-15-14-13-12...

and a 54-12 is nearly a 53-11...

The extra 4 teeth make a hill to walk a hill to ride, one thing of interest is that grades this size most pros run a 39-21, which is the same as a 42-23 approximatly... I am not a pro and do not have the power (yet) to push that gear up these hills...