I've setup Mach3 to drive the 4th axis tangential to the XY plane. This feature is used by vinyl cutters and such where the tool's orientation must follow the direction of travel. This includes lifting the tool before large changes (>45°), and lowering it before continuing.
This setup allows me to test my 4 axis servo controller in a "real world" situation. The motion appears a little jerky, but this appears to be Mach3 coming to a full stop before changing the 4th axis' direction (The RoadRunner test is not good for this since it's composed of lines and not arcs).
I've started making the mounts for the motors, but there is more tuning and testing to be done before final mounting of these motors on the mill.
When I'd picked up the motors, they had some heft. So out of interest, I put those motors on the scales... a total of 3kW (4HP) and 16.5kg (more than airline carry-on allowance).