Mike here from Streamside Furled Leaders Here.
I make about 8,000 leaders / tenkara lines a year.
My motor runs at 20,000 rpm but has a variable speed control like the pedal on a sewing machine. I don't think I have ever had it over 5,000-6,000 rpm while furling. I have had it almost wide open when re-spooling bobbins. The furler that Michael Hackney made for me has a gear ratio of 1 to 1. I like the added control it gives me.