Actually, I doubt that Esslinger can supply flow curves. I worked with Dan Esslinger as far back as the mid eighties, I became very close to the family and they were a great help with my engine program.
If the pump that you refer to is the remote pump the midget motors currently use, I have some knowledge of how it came into being.
This all occured during my tenure at Ford Engine Engineering in the 2.3L OHC design group. The Ford water pump is nothing more than a paddle wheel, and I was looking for an external pump for my turbocharged 2.5L engine for my Merkur Land Speed Efforts.
I found the external mounted 2.3/2.5L HSC engine water pump. I was able to have it flowed in several configurations, Restricting Inlet to 0.98" and 0.84" which is the id of -16 AN braided stainless hose.
The pump has good flow and there was NO cavitation, up to 9K rpm which was the highest we tested. (pump speed) This test was in 1992. The only data I have left are some hand written notes I made at my design intent.
At the design point of 0.84 inlet restriction and a thermostat.
9000 RPM it required 5.90HP Flow was 74.3GPM at 302f H2O
Pressure B4 thermostat 67.7psi and after stat 39.9psi.
NO I didn't run at this point. Since I had all the data, I looked at running 1:1 down to .3:1 pump speed. Actually back then I had too much of an OEM mentality that I was targeting 7000 RPM. At that point flow was 38.2 GPM at 47.9 PSI.
Dan used this pump and data supplied by Ford SVO in 1992 on their Stadium racing truck. SVO supplied a few pumps and all the data I had.
Since that time Dan basically reverse engineered the pump castings and produced his version of the design intent. I don't believe they had water pump flow capability. They would have used data I supplied.
With the time passing, two fires in their building, and sale of the company to an offshore owner, I'm guessing that much of the data and history of Esslinger Engineering/Racing has been lost. BUT the remote pump they have for sale is a very good copy and performs well.
Bottom line USE A THERMOSTAT and you should be fine.