Greg,
The decision about using city water (and pressures) or to pump from your holding tank is usually based on how your converter designed the water system. A conventional motorhome may have been equipped with a single low flow water pump so in that case municipal water would be the preference. But I think the Prevost converters today want to have a water system that is capable of handling multiple uses without any degradation in water flow so they are being equipped with high volume, high flow pumps so someone taking a shower is unaffected by someone flushing a toilet.
Mark is correct about not worrying about water pressure and I think you will agree the variations in municiple water systems will make it just nicer to use your pump.
This is true, but largely dependent on the type of toilet being used as well. If it is a direct drop Sealand, Thetford, or Microphor Electric toilet, little water is used for flushing, so it doesn't really matter which approach to water system design is used, but it does matter if the toilet is a Royal Flush "Water jet pump" toilet. The Royal Flush toilet takes high velocity water to create the venturi vacuum in the volute of the bowl, and the "jet pump" principle of evacuating, macerating the toilet bowl contents, and pumping the contents to the waste tank. This toilet takes a full 1-inch water line plumbed from the pump outlet through the flush valve and directly to the toilet to accomplish the flushing. An accumulator tank can be placed at this juncture in the fresh water system so that the toilet can often times be flushed without the pump turned on as long as city water pressure was high enough, even if the flow rate was not there through the smaller diameter city water hose and the protection regulator and smaller fresh water piping lines, but this is still not a "sure thing" to flushing without the pump. The sad thing was, regardless of what the coach converters wanted to put in for a toilet, the Royal Flush became an "industry standard" at a point in the late 90's, and since then, all the big converters have utilized them.
Ben Cummings
U.S.A. Luxury Coaches, LLC
Clearwater, FL