Hummmmmm the smell of electrons are in the air.
Dennis
The smell of electrons are OK but the smell of the black smoke when things go wrong is hideous!
Denny, I don't have a lot of experience with exactly what you are up against but as long as you are not tied to competition rules where you must tailor the aircraft to a specific length of lines, finding what works best for this airplane is going to be like choosing the best prop for a certain plane motor combo.
I think you will need to make up several sets of different length lines and try them all.
One thing that has not been brought up and needs to be considered is that just two feet can make a very noticeable difference. This is especially true at longer line lengths. What I am trying to say is that I would not go right from 42' to 52' in one step.
In fine tuning this wild beast (which has my attention!) You might find that you need to tweak the engine offset or rudder to get it to fly on the 52's. Who knows, you might find you like it best on 50' lines.
It also sounds like you might have propeller issues as well if the motor is as you say. If you know without a doubt you have a large surplus of power, there has to be a level of inefficacy somewhere. I am sure you will be able to wade though this and have a massively rewarding experience!
I look forward to seeing more about this project, Robert