Hydronic Circuit Simulator

After reading a post about the Grundfos 15-58 I was trying to make a comparison to my current circulator, A Taco 007-F5. When I compare the curves from the literature on each website at 10 feet of head the 007 comes in below 5 GPM(tough to read the scale to get the exact number). The 15-58 shows 1.86, 5.76, and 9.07 gpm at the same head for the three speeds. I converted 10 feet of head to 4.32 equivalent resistance and input that into the hydronic circuit simulator, 007 shows 1.67 and the 15-58 shows 1.69, 2.03, and 2.21 GPM. The 15-58 shows a large difference in GPM capability between the pump curve literature and the results of the circuit simulator. Am I doing this wrong? I am still trying to calculate exactly what circulator I should use. A 1950 B&G iron 1.25" Monoflo system. I was trying to determine if I might benefit from a larger circulator and was trying to calculate how much more flow a 15-58 would produce in the same circuit as a 007.