Herbie overflow - what size?

[Sunee]

Hi. I am planning an upgrade and need some help with the plumbing before I order the tank. The new aquarium will be 30x30x18" (about 60 gallons) with a 20 gallon sump. Return pump is a Tunze silence - with head and friction loss I should be getting about 350 g/hr with 3/4" pipe but I will probably dial it back to less than 300 g/hr as it is adjustable.

I am planning a Herbie overflow and would like some advice on the size the overflows should be. I have done a lot of reading but there are so many opinions on actual flow rates that I need help! I have read anywhere from 165 to 660 g/hr for gravity feed for 3/4"!!!! Is 3/4 appropriate for the flow rates I want or is 1" better for my setup?

I really appreciate any advice I can get. Thanks in advance!!!!