The jerkiness probably is centered on the user, not the control results.
I'm using mach3 on a gantry router that travels approx 4x4 feet. I use bobcad v21 to program more complex paths. Anytime the path transitions from one line to the next, for example: g2 then g1, or g1 to g1 transitioning in an angular move, the control comes to a complete stop between each block. Yesterday I had to cut a convex portion of a sphere, and bobcad wrote it as thousands of straight line segments, resulting in a path that starts and stops thousands of times. Not smooth.
I scanned through the different settings available, and didn't see anything that pertained to this, but I have to confess I haven't checked the manual yet.
I know that with our Heidenhain TNC360's, there is a parameter you can set, which limits the maximum angle you can transition before the control has to stop motion, but I don't know if this is a similar option I am missing with mach3.