I read that Sequence pumps run more effecientially when they are throttled back using a gate valve and not tee'd off. When I have a free second, I plan I redrawing my design with the refugium over the sump similar to how chrisguy has his set up.
Heh, well that's kinda true magdelan, but it depends... Ok here goes. A sequence pump is a good example of common high-head centrifugal pump. These pumps consist of an electrical motor which is connected via a driveshaft to a water pump (in this case centrifugal).
Now, the properties of the pump (thing that moves the water) indicate that a certain amount of work is required to move a volume of water against a specific amount of pressure drop. Given a series of different pressure drops (head pressure), we get a series of different flowrates, AND electrical power used. This can give us two curves. First, the "pump curve" aka flow curve or pressure curve. This shows how as head pressure increases, flowrate decreases, and vice versa. Sequence was kind enough to list all their
pump curve data for us. They didn't actually make the curve, but with excel or similar graphing program you can. The pressure curve usually has head pressure on the Y axis and flowrate on X.
The second curve you can make is the "efficiency" curve. It has pressure drop on its X axis and watt draw on its Y axis. So an example, lets use the Hammerhead model pump as I think I heard it's name reccomended before. Head pressures of 0-16.8ft all have corresponding watt draws in the 350-375 range and flowrates of 3000gph or higher. At the next data point of 19.6 feet of head, watt draw drops to about 325 but still a high flowrate (3000gph). Thereafter, the pump portion of the assembly starts to reach it's limit as far as providing flowrate is concerned. When head pressure increases to 24 feet, the flowrate really tails off as the pressure is too much for the pump to overcome. This corresponds to lower motor speed and thus lower watt draw 265 watts in this case.
So yes, you are correct that increasing head pressure can lower the watt draw but also at a considerable cost for flowrate and very high pressures right at the nozzle, keep that in mind. If you wish, you can still tee off the main return line provided that all lines are controllable with ball/needle valves, you can still get your pump dialed in to where you want it.
My final words of concern with pump choices is to not push the envelope. While the watt draw lowers with those high head pressures, keep in mind, the pressure is getting quite high. To the point where home-made PVC pipes and pump threads done by not the most experienced of people may start to fail. Furthermore, I never believe in running a piece of equipment right near the edge of its design. And heck, if you want a lower watt draw, lower flowrate, and lower pressure, just get a smaller pump

. So my advice to you magdelan is to first figure out how much head pressure you're going to have using some of the calculators on the main page. Then, consider how much flowrate you want, and choose the pump that gives you that pressure-flow somewhere near the middle of its operating range.
Sorry that was long-winded but I hope informative