Your right the RMHV and DDCSV are more or less the same.

I'll use a pot connected to the sprint board for speed control for now.

After a bit of digging on the internet and head scratching I *think* I've figured out why the speed control was set for 50v. I think that the 50v is the voltage from the tacho at max speed rather than the max output.

But worried about your comment regarding the motor failing taking out the speed controller, what tests can I do on the motor to establish if its good or not?