Currently mach4 and mach3 have the same trajectory engine. I have done a lot of comparing of mach and 2.7 because I did a lot of the testing of the 2.7 trajectory planner. Mach always ran faster flat out but it cut corners and violated acceleration constraints in my testing. Playing with mach3 trajectory controls I could get a similar path (it doesn't have a way to say follow the programmed path within x amount - it is a setting on how far from the segment end points to start blending - which is odd) but it still violated acceleration constraints.
Sam