To put a nail in this I've made some videos. I tested three engines, one with ERR (CC-M), one with TMCC/Odyssey, and one with Legacy/Odyssey II. For the ERR I made three videos, one 32 step, momentum L, one 32 step momentum H, and one 100 step. Contrast this with the TMCC/Odyssey loco where I did two videos one with momentum L and one with momentum H. Last I threw in a Legacy loco for good measure in 32 step (hit L on CAB-1) and 200 step mode (hit H on CAB-1). All of these were filmed while using an original TMCC Base and a CAB-1 remote. As you can see in the video - the momentum seems to have little to no effect with the CC-M. It's hard to tell for sure because my thumb may not be moving at the same speed.
However, with the TMCC/Odyssey loco, changing the momentum has an absolutely drastic effect. Any change in momentum on the ERR board might simply be that selecting H put's it into 100 speed step mode. It says that's reserved for the C11 and C13 revisions, but who knows - maybe Lionel updated the code in the C08 they are shipping now. This might be the case if they are shipping R4LCs as R2LCs.
CC-M 32 step momentum L:
CC-M 32 step momentum H:
CC-M 100 step:
TMCC w/ Odyssey momentum L:
TMCC w/ Odyssey momentum H:
Legacy 32 step:
Legacy 200 step
