I did some googling and found this...
High Speed CNC milling machines working on 3D surfaces in any materials produce a finer surface finish and higher accuracy in less time that the traditional milling machine. Acceleration is the most critical factor that affects the high speed machining. Since one or more axis are always increasing or decreasing velocity in a 3-D cut, ultimate feed rate is directly related to acceleration
This leads me to think my acceleration rates are what to look for and for some reason mine are too low on 2 machines?