I Have just ran my Mk3 version against some top opposition(A main) in a regional UK championship (SLCC) and I can honestly say without any doubt I was not short of power on any part of a known UK "power" track!
In fact I back to back tested with another well known speedo I own,I prefered the SXX due to its smoothness of throtle and importantly the very impressive consistant brakes
GM 13.5(12.3 rotor),10 deg can timing.Punch/feel 6,boost 9,FDR 6.66 with perfect temp's and not an ounce of problems...unlike others makes that were gogging,stuttering, loosing profiles, dropping into sensorless mode or left motionless on the grid
.....Ive never heard so many F&@*'s or seen so many heads burried in lap tops..not me,just a quick "juggle" and balance with punch and boost
Ps this speedo seems to match well with the torquy type motors.