I have 190 to 250 on a 50 gallon depending on how dirty it gets. I'd aim for 300 to 450. The test is that the heaters (and chiller if you have one) in the sump keep the display tank the same temp as the sump's water temperature. Flow is for wave makers not returns IMO. slow returns are quiet, less issues with roller filiters and micro bubbles, etc. no reason to go heavy flow.
Getting a pump that is rated for 900 gph and is adjustable with flow (DC) or about 700 gph (AC) i think would be good choices. This lets you run the DC pump at say 50% and it will be quieter (noise is usually most notable at 80% or more) and then increase power if needed if it gets dirty. The A/C pump you can add a gate valve on outlet side to lower the speed or increase as needed.
the higher gph above also factors in the reduced GPH cause by plumbing.
I like Ehiem for A/C. Last of a decade and probably longer. Pretty quiet. Not expensive
The jabeo seem to have mixed reviews for reliablity. But you could have a spare for the cost of other pumps!
The sicce looks pretty good on DC front for cheaper.
I really like ecotech's mobius app and adjustable flow on the vortech and assume there return pumps have something similar.