Hey Glen ,,
what about the other guy using the 19-11 apc
with a standard 1.7ys non cdi
I have seen no difference in performance between the CDI 1.7 and the Non cdi using the 19-11 APC
other than a smoother run at Idle and virtually no smoke trail.
the CDIwill not increase your power!

Lets notmix Engine tuning with Prop performance <G>
his engine was not performing well.
Both my 1.7 non CDI`s turn a 19-11 with no effort
Also TheYS I was using had 6 flights on it when I arrived and was not fully broke in.

I have run the 19-11 ,18-12 and 18-11with no problems all three are good props i love them all,
it`s a matter of selecting one for the airframe and flying styles
my suggestion is to buy all of them and choose the one that fist your setup best.
Bryan