Second calibration cube, but this time after printing and installing an x-axis tensioner.
Much better overall, but I'm still getting a wobble in both the x and y-axis. Therefore my next step is to print and install a y-axis tensioner. I also noticed after the print that the bolts had come loose around the extruder, adding further wobble to the x-axis. That has now been fixed, so hopefully the x-axis wobble will be reduced in the next print.