Yeah, it overflows and goes into the overflow, then goes down a tube into two socks to filter out large waste, then it goes into a refugium with a deep sand bed and then it goes into another compartment where a 700 gph pump pumps the water back into the tank.
The venturi valve in your protein skimmer will tend to use energy enough to reduce flow by about 20% of the line feeding it.
And any centrifugal pump can be reduced using a ball valve on its outflow without compromising a pump.
So as some others have said, better to get the stronger pump, and if need be, throttle it back, than a smaller one.
On my freshwater tanks of around the same size (with protein skimmers) I use 2400 GPH pumps
(because freshwater fractionation takes a bit more agitation than salt water).