OK, thanks for the suggestion, but it is interesting to note it’s now much worse with the newer firmware. Marlin is meant to be able to process arcs, though the old version did sometimes stutter once on some runs of the “big” circle, the new one stutters at every arc-end. Probably too many things happening and buffers emptying causing stalls. But it’s a trade off, really, by turning off arcs you end up with lots of code for only relatively small machine movement. This can have its problems too.
I might stick to GRBL for everything except 3D printing. It runs both the little and big circle tests smoothly and it’s very consistent. Marlin is new to me, I usually use Sailfish and/or GRBL. Thanks again.