Trying to pick the right return pump

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OK...I'm looking for the right reurn pump......75 gal FOWLR tank and a 30 gal sump.
How much flow do you guys think i should go for? I was thinking 700 to 800 GPH,but was told that might be too much with a 30 gal sump.

Herbie style overflow,with 2 x 1 1/2 inch bulkheads
Probably going with 1 of these http://www.aquacave.com/eshopps-psk-...tank-2859.html

Any thoughts? Any help would be welcomed.

Thnx in advance

Doug