I’ve since changed out the steppers for higher torque ones. I’m still tuning with those, and I’m not convinced it made a difference. The higher weight of the bigger steppers (they’re about 3 times as long as the stock ones) looks to be offsetting their higher torque. They also have 8mm shafts, which made getting the right 21 tooth pulleys a little more difficult than I expected.
Anyway, significantly higher speeds are available if you’re willing to try. It does make a difference in your cutting times by greatly reducing your time in rapid movement. The machine will move around more if it’s not held down well though.