Especially with your less common prop, there is only way to know for your specific setup, which is to do some testing. I have seen a very wide range of reported glide speeds for 9's. Ratios may be similar, but I assume you'd still want to know what speed to get that ratio.
....this from a guy who has done NO flight testing....
is there more than one?
can the MT fail in coarse, and fine pitch?
I would think you want best ratio, meaning DISTANCE....
and also minimum SINK, where distance is not as important as time aloft.
( ok, I am hard pressed to think of an emergency where you are above an airfield, and want more time aloft!)
I will do some specific flight test on that matter but for the moment I?m tryin to get the basics of my Foreflight filled out. If I start with an average number it?s agreat start.
If the electric mt prop fails it will stay at the current pitch.