Great question. And just to preface my answer - I'm very likely different than most BEAST users. For the most part, on any of the 3 BEAST tools - I'm on speed setting 6 for everything.
With the CBEAST - I will often place tape around the tool body to keep the speed dial on the 6 speed setting. No time for bumping it by accident and dropping to a lower speed.
With the BEAST and the Supa BEAST - on on speed 6 unless I'm doing some finesse work on edge and even then - I'm on speed 6.
And I can't remember ever using the tool on speed 4 or lower. The BEASTS smooth out at speed 5 and faster.
And for those reading this into the future, I've switched all my CBEASTS and Supa BEASTS over to the optional 6" backing plate so I can turn and churn larger pads. These tools have the power, might as well take advantage of it. Plus, with the 5" backing plate and matching small 5.5" pads - the tool feels "wonky" to me. A larger footprint eliminates the wonk.
Just finished straightening up the garage and going through all the microfiber towels and buffing pads. Getting ready for our big 3-day class. Time to call it a day. I'll be here late tomorrow after work and probably most of Saturday sanding, buffing and coating the 1967 Mustang. Had to bring some semblance of order to the shop first.