latetonite:
please explain how VNAV can maintain a PATH, if limited in speed?
As VNAV PATH initially increases speed in descent from ECON SPD, up to but not exceeding KIAS 330 and/or M.081
If you want to prevent VNAV reaching that speed when (very) high on profile, speed brake can be used to allow VNAV to dive but without the speed increasing too rapidly (good airmanship...).
Either way, it would make sense that when VNAV increases the speed to adjusted a VNAV PATH profile in the FMC with a higher speed so not to allow VNAV to dive too much but to reflect the remaining energy contained within the aircraft.