I wanted to measure the realized torque from the qdd100 servos, so built up a simple fixture that let me attach a 1m long pole:

I used that to push down on a digital scale and figure out the actual torque mapping.   The plot of phase current vs torque looks like:

I've got some more learning to do to fully understand why the torque constant is lower than I expected, why it drops off as much as it does at higher currents, and why I have the variability I have between devices.

Here's a video showing the testing: