I have 2 montiporas that are growing close to that rate, a monti cap and another that looks simular to yours. I have some other branching and some encrusting monti's that are growing at much slower rates.
To me it looks like a high rate, definetely a healthy rate... keep doing whatever it is that you have been doing, it's working!
I have a 2 inch monti frag that I bought over 6 months ago that has grown maybe 1/4 inch in 6 months. I guess my tank is not doing to good.
_________________ g13 diesel