Energy use is linearly proportional to flow rate so this is one reason that the WFE-2 uses close to the same energy as your current pump. However, the WFE-2 should have slightly better efficiency so it should use less watts.
Payback for a new pump could take quite awhile since you have already invested a lot of money in the WFE-2. There are a lot of factors when determining cost but the energy use for the Superflo should be about the same as the Whisperflo on high speed. However, on low speed, the flow rate goes down by a factor of 2 and the energy use goes down by a factor of 4 so in effect energy efficiency (GPM/Watt) doubles on low speed which is why a low speed pump saves quite a bit on energy use. Your savings will depend on the cost of your energy, the amount of time on high vs low speed and the plumbing system losses. Without all of this information, I couldn't tell you exactly how much you would save but a rough estimate would be about 25%.
Another option would be to simply replace the motor but at this point, I am not sure that would be worth it either unless you can sell the old motor for close to the cost of the new motor.
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