I assumed with a compact double, I'd have to change out the whole crankset which I was trying to avoid. I hadn't thought about the BB. I suppose if I need to change the BB out anyway, I might as well do the whole crankset with a compact double and 12-27, as mentioned.

How big of a problem would this give me with the 105 derailures? I'm trying to avoid changing out the whole component group, but my goal is improved shifting.