Go to this page and look at the head loss calculator.
http://www.marinedepot.com/ps_Aquari...e_supreme.html
A Mag24 at 15 feet which I is about the distance I have with my 180 setup is moving 650 gallons, compared to 2400 at 0 head.
This link is for Sequence pumps:
http://www.premiumaquatics.com/seque...rflowcurve.htm
I have a Marlin and at the same distance am getting about 1600 and using the same amount of power. The marlin is an external pump so there is less heat transfered into the system. Now in the winter that heat transfer is not bad, but in the summer, not so good.