Hey dayglow,
I have never heard the Certaldo 2 speaker. My hunch is for another 5K you get another level of refinement/polish to the RF house sound. If you like one of their less expensive speakers, you just get more as you move up the line. Remember some of their larger physical models might not do as well in a smaller acoustic space.
If you would want to hear the Arno 40s during Axpona this year, I don't live very far away from the show. You are more than welcomed, if they don't show the 40's at the show. They probably will show the 40s being that its their newest model.