Overflow size & return size & calculating actual return rate after head?

3/4 at gravity tolowpressure is going to run about 660 pH at a flow rate of about 6foot a second. Typically we Goethe doublenyour return size rule to prevent overflow or restrictive gurgling or pipeknockoing. With 1.5 inches of over flow you will have more thanenough flow.
Other rules 10x capacity an hour for flow in tank. I Stoll think that high but thats just me. ,y 75 runs at about 10 x the flow my 40walkabout 3-4 ad does just fine... thrower flow is better for good deal of systems like skimming and algae scrubbing...
You area about 5x your capacity. I tank this will be just fine for now and you can always upgrade later.

 

For what it's worth, I'm a firm believer in having sump water linger in the sump, ie. the longer the water stays in the sump, the more opportunity for the skimmer to skim well...GAC and GFO to work...chaeto, etc... In tank flow should be handled by powerheads, not the return(s) flow. I put a valve on every one of my return lines so that I can control the flow. Restricting the flow on the return line (pump) doesn't hurt the pump, IMO. Again, just my 2 cents Justin.

 

One the many reasons I have come to respect sponge! She is dead on here.

 

This is a tried and true method, my 40 runs a setup like this. My 75 has an rdsb
In a ten.for a similar purpose and my fragtank has two tens over it one for anemones and one for shrooms. Again the pump you have should work just fine and any volume of water you add will stabilize system, any volume of rock will add filtration.

My 40 has a pretty low return rate And has been running fine for a long while. If you really feel the need to upgrade pumps you should look at fountain pumps which are typically designed for head pressure. Usually a little louder though.