overflow size?

[marks69]

hi all, i'm seting up a 120 long this weekend. i would like to go with a wet dry but need to figure out how big of an overflow and return pump i will need? the tank will be cichlids for now. the sump will be a 30 gallon tank. i'm thinking 600gph overflow?
in the future i would like to go salt but for now there's no funds.
thanks all
mark