I usually mill PCBs around 40..47ipm. I've milled at 55ipm before, however I have to have spindle RPM max'd (loud) otherwise I chip the fine tips off.
Yours is looking good, but your limitation is with your "acceleration"... not max speed. If you're using Mach3, have a look in Config->Motor Tuning... what acceleration have you got? Find out what the max is before it skips steps on acceleration and deceleration, then bump it back to something reliable.
Next, check the General Config and make sure you have Constant Velocity mode as the Motion Mode. Then go to Settings (Alt-6) and make sure CV Distance has a green light and the CV Feedrate light is off (important).
Now machine that same example.... if you were impressed by that, you going to spin out when the acceleration is tweaked
