I'm not really a sump guru, but my understanding is that you will need a pump that can handle 1200 gph
at the head you plan to run it at. I've just recently set up my first sump which is running one overflow at 600 gph
. After asking around I was told by many people that a Quiet One 4000 was perfect for this application. After set-up it ran perfectly the first time. It's running wide open (have a ball valve in line but wasn't necessary to restrict flow at all) and it keeps up with the water from the overflow.
Again, I'm not an expert, but it seems to me that you have to go with 1200 gph
minimum for the given head and the closer to 1200 gph
the better. Otherwise the pump won't keep up. On the other hand, if you go too high-powered then the pump will drain your sump faster than the overflows will return water to the sump. In that case it would be necessary to restrict return flow using a valve, but that will shorten pump life and produce noise. This situation can also produce problems with micro-bubbles. Anybody else please feel free to correct me as I'm still learning this stuff too