I just did a little asking around here where I work and got refresher on power. As I though, most of the inexpensive kilowatt meters (which you may have) only measures "resistive" loads. Which depending on the device being measured can be 100% accurate OR a lot less then the true measure of power used. The whole subject get can confusing if you not confortable with the math and details. But needless to say the electric company does not charge you by the resistive calculations. Devices such as pumps that have large coils in them are described as inductive loads and will cause the voltage and current waves to move out of phase from each other which throws off these meters. Most accurate way to make a measurement is to look at both of these curves on a scope and calculate the vectored load. And there are also automated power vector meters. But in the end these are expensisive. So I would probably trust the manufactures chart the most. In that case if you say you are experiencing about 10' of head then your flow most likely will be about 2700gph which sounds accurate to your description. And your power will be about 320 watts............ Sorry, it would appear the old axium is true, nothing comes for free,
Jon..............