First of all Tony, you have done a fantastic job in doing this work for all us would bees.
The placement of the gauges could not be better. There is a lot to be learned from these test that you have done.
Looking at the first graph, without the thermostat the first interesting point is at 2500/3000, when the pressure at the top hose and the inlet to the pump start to separate. The thermostat is between these two, so it would seem that is a restriction as the difference between the two pressures has grown at 5000, to about 10 psi.
The other point to see is the way the pressures between the top hose and the left side of the engine block, are separating at 2000 becoming larger to 3500, then increasing pressure up to the same, as the left side output. By rights these two pressures should stay the same, unless there is a restriction between them. The only bit there is between them is the junction of the right side block outlet.
Other than that the inlet pressure becomes more negative while the outlet pressure becomes more positive, as the revs go up, showing that there is a restriction in the circuit. As Dan said the pressure around the system should be about the same.
The second graph, thermostat in and out, hits us right in the eye that the thermostat is restricting the inlet to the pump. At 4000 the top hose pressures show the difference between the two increases as the rpm goes up. With the thermostat out the top pressure mimics the pump inlet, minus the restriction of the radiator. With it in the pressure in the top hose is rising, as the thermostat becomes a restriction between them. We can see that reflected in the pump output that is rising as the pump can pull more water in, to pump a higher pressure out, without the thermostat.
There is more to be deduced from this, as we look longer.
Harvey.