Absolutely no doubt in my mind that sump should be as big as you have room for!
My sump...refugium and frag tank with 200lbs of rock...will be 2 200 gallon tanks on 225 DT.
Mind you not full to top of with water but would have 1000 gallon sump if i could!
Small sump is like having a Ferrari with weed eater engine!!!
Why?
OMG....you will be able to feed tank whatever you want when ever you want with no ammonia or nitrate repercussions!
I understand some of us have space limitations

But think of the biggest sump you can fit...then times by 4

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The Great Barrier Reef! ....what size sump does it have?
The Great Barrier Reef!
Sump....tried to calculate but not a calculator big enough for all the zeros on water volume of oceans!!!
Protein skimmer...all the Australian beaches and the rest of the world!
Refugium....well i think you get it

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Don't have a fancy tank to show you...but will in a couple of years

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You think the display is fun???
Wait till you have unlimited room in sump!!!!
I think for every 10 gallon of display...if you got room...you should have 100 gallons of sump!!!
If you are having more fun in your display then your sump...its like loving your radio in a Bugatti...instead of the engine????