30/50, 40/60, or 50/70 it doesn’t matter. The same showerhead will still flow less water when you are at the low end of the pressure than when you are at the high end. When the pressure to the showerhead varies, so does the flow rate and temperature. What I hear is when the pressure and flow rate is low, many times the tankless heater won’t fire off. When the pressure and flow is high, you need to add more cold water to the mix. Tankless heater or not, varying pressure and flow in the shower can make maintaining the water temperature a problem. This is unlike city water pressure, which stays fairly constant.
Of course all the people I hear from have this problem. So I don’t know how many people do not have this problem or just learn to put up with it. If you have this problem, I know constant pressure from your pump will solve it. If you don’t have this problem, then constant pressure from your well pump just solves a lot of other problems.