I used a 1/2 cove bit, but I had the speed set slow - 20 inches/minute I think. The real tell came from when I tried to cut a circle. The top and bottom (in the Y-axis) have flats on them. Searching for this defect on line leads to suggestions of a loose pinion gear.
The other bit of data I have is that I could measure very accurate positioning in Y when I did large or small moves. However, when I did a series of 10 small moves the right side lagged by ~0.060".