Im putting a Pentair Aquatics Pump in the wet/dry im building. Its all in what you need for a pump, You should have a pump thatll do as much GPH as your overflows do, if not a lil more.
to choose a pumps rating you need to know a few things.
1.)how many times do you want your tank to cycle per hour (the more heavily stocked the more you are going to want it to cycle)?
2.) how high is the water going to be pumped from the sump back to the tank (head height)?
After you find these things then you can look at the manufacturers guides and you can choose an appropriate pump.
I have a mag drive and it is great. Very quite and havent had any problems with it.
I thought the general rule of thumb was to "turn the tank over" 3-5 times an hour. I have a 180 and am using Little Giant pump pushing 1200 gph. Its got about 3 ft of head on it so Im thinking @1100 or so per hour
what type of aquarium salt, fresh, or reef. little giant, iwaki, quite one will work great, a 1200 gph pump based on head of 5ft will give you about 750gph of flow through 3/4" tubing or PVC pipe if it is pressure rated