Most LS guys in the US just use -6 from pump to rails.

I flow tested my as installed fuel system -8 feed with -6 return and it supported 486lph measured after the FPR and via the -6 return line at 60psi rail pressure
Flow would have been higher with better battery voltage.

I dont imagine too many cossies needing that sort of flow ability.

And the biggest restriction in the system will be the FPR anyway.

Plus, how big are the fittings on any fuel filter ? How big is the "rather tiny" outlet on the pump ?

Unless you have a multitude of bad bends, -6 will be more than adequate for 99% of Cossie engines.