Overflow box/ Return pump question

First off, I am doing a 40 gallon breeder tank with a 20 gallon refugium. I am thinking on getting the rio 1700 return pump that puts out 642 GPH. And a Eshopp pf800 overflow box that puts out 800 GPH. Does that seem like a good combination? Or should the pump be able to put out more than the overflow box.

 

the head rating is the really important one. It's what tells you how high the pump will go. I personally think that would be just fine.

 

even with the overflow box pumping 800 GPH and the return pump pumping 642 GPH?

 

I think I would be ok with that and you can always put in a gate valve to slow down the pump, but are you sure it will really be 642 to the tank? what is the head on the pump?

 

According to every website that I checked, the rio 1700 pump has a flow rate of 642 GPH

 

But at how high? how much room do you have in between your sump and DT? I have a stand with 2 tanks, one tank over the other making it about 4 1/2 feet to my top DT from my sump. So if I got a pump that pumped 642gph with a head of 9feet I would approximately be getting 321gph to my DT. Most pumps don't slow down at a even rate so it probably would not be exactly half, but I think you understand what I mean

 

I haven't made the stand for it yet, but I just checked and it will probably be around 4 1/4 to 4 1/2 ft. So if the pump will probably be restricted to around 321 GPH then I should go with the Ehopps pf 300 overflow box that pumps 300GPH.

 

it depends on the head rating of it, if it's rated at 642gph 20 feet you will something like 481gph (3/4 of 642) some pumps are high flow low pressure and others have more pressure.
I think most pumps should have some info about the flow to pressure curve that they work at.
Maybe some one else can explain it better than me

 

I don't know. It's not you, but I'm getting confused. Here is the link to the pump.
Taam Rio (Rio+) Powerhead/Pump

 

Heres a flow chart for Rio pumps.
Rio Flow Chart - Rio Pumps

Even though the chart says 352 at 4' that is on an unrestricted run. Return pipe diameter, 90 degree ells, valves, etc. all play a part in restricting flow. So in all actuality that pump is probably only putting out somewhere in the upper 200's gph after headloss.
If you can afford it look into a Mag 7 or 9.5.