testing results:
50mm^3/s flow, @ 500mm/s print speed. 0.4mm nozzle. 80mm/s travel speed to allow just a moment of melting time for pre-heating the plastic. Each layer of these has less than one nozzle melt zone of plastic volume. This shows how much speed is being left on the table by constant flow limitations.
obviously needs some more tuning for the start/stop but the instantaneous flow is there.