First suggestion is you re-post this thread in the Pump Engineering Group so you can get help from pump experts like Pumpdesigner.
When you say "high end", my undersatnding is that you run the pump at close to the dead head--high pressure, low flowrate part of the curve. This is the operation we should do our best to avoid.
1. It is normally far away from BEP - best effeciency point. You waste energy.
2. Flow recirculation in the volute is very high, flow is not stable. That often causes vane and case vibration and significantly shortens the pump life, especially the life of the bearings. Actually I've heard the case that bearings were broken when a pump was running at very low flowrate for a period of time.
Many menufecturers have recommnedation on minimum flowrates for their specific pumps. It is important to follow that recommendation.
