Jerking and banging noises makes me think of some kind of binding issues to do with the slides of the machine. This could mean the center of gravity of the head is too far off center of guide bearings that are too close together on the slideways. The amount of clearance that the bearings have could also be a concern: a little too much and they will lock easily due to the available tilt in the system with an offcentered load.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)