Best CL Pump

[Hdhuntr01]

Building a 120G and the tank already has a 1" Bulkhead drilled in the upper back of the tank so I want to use a closed loop. The PVC pipes will be 1" and most pumps I have looked at have a 1" Intake and 1" Output. So my question is what is the highest GPH pump I can use with just the one 1" intake? I can run up to 4 returns which will run over the top of the back wall. Also thought about using 2 SCWD's...

Suggestions based on experience????