jimmydee-
I've been reading Pond Boss for some time now, and thought I'd finally chime in. My background is in large scale aquarium(upto and including public and institutional exhibits) design and construction.
I can tell you from experience that you will greatly reduce the efficacy of your sump pump and it's longevity by reducing the size of the return (outflow). If that idea is truly something your interested in, you'd be best fit to find a unit that is rated for high head pressure. These type of units are already designed with a smaller return than the suction (intake) side.
High flow units have the same size return as they do suction. These are not the ones you want if you're looking for high pressure out of the return.
Not to mention, as the guys already have, that moving water takes more energy than moving air. Water is heavier and takes more energy to move. Larger pumps require more electricity, which equals to more dollars out of your pocket. Moving air via compressor, takes a lot less energy, and moves the water for you as a desireable "side effect." (even though in our case it's actually the end result we're looking for from the start).
If there's anything I can help you with, please let me know. Good luck with whatever you decide.
