Harold Kestenholz
Good points, Sylvan. A Licensed Master Plumber is most likely to understand the problems of laminar flow and pay attention to the details necessary to prevent it in the piping to reduce noise and replacement of pipes and fittings.
The tables used to design small tube systems pay attention to the velocity of water in the pipes. As you say, velocities of water below 2 fps are useful in extending the life of the piping system. Velocities over 5 fps cause noise and accelerated erosion. Circuits that are too long create uneven heat and inadequate velocities.
Velocities in copper tube radiation effect the output of heat from the fin tube. Cast iron baseboard is a larger, unrestricted vessel, where velocities can not be too high and low velocities do not affect output.
Proper design of a system does not have to be a hit-or-miss situation. There is plenty of design information that has been given to a Licensed Master Plumber beside the experience.
