I did the regulator addition to my 161, and changed the cables on the jamma extender for RGB and Sync to mini coaxial style, using the shields of each as the GND for video, and now the rolling has stopped totally. Previously, before the regulator addition, i'd just changed the cables for thicker ones, and although that helped with the rolling, it left the small bent area at the top of the display - now that is gone. in fact, it'd say the picture is as good as direct from the MVS now, after slightly adjusting the contrast on the tube.
Keeping in mind that the MVS direct to the cab's jamma while running the 161-in-1 was always solid, and even the MVS mounted directly onto the slot on the jamma switcher is still twitchy, it's safe to assume that the 6-way jamma switcher, combined with the extenders, causes enough of a drop to mess with the sync & colour levels, and require a re-calibration of the monitor itself. I see other boards on the same setup ALSO look different - for example, a Williams board (originally non-jamma) looked darker, and the ST-V lost some contrast etc., but did not start rolling.
Anyone using a multi jamma switcher & MVS with the 161 might get the same sort of issues, but i'd expect some penalty somewhere when using a jamma switcher in all cases, there is defo some loss.