Out of curiosity I tracked the focal length used for portaits over a four week period using the 70-200 f/2.8isII. A staggeringly high percentage were in the 120-150mm range. So that quickly turned my attention to the 135 f/2. AF is very fast but doesn't seem quite up to the 70-200 f/2.8isII.
After autofocus microadjustment (AFMA) on my 1D4 and 5D3 it's settled in just fine delivering stunning files even at f/2. BTW the AFMA for both bodies needed -9.