Fueling & Injection - Whats the max HP from 3/8" fuel line w/ret

Whats the max HP that can be squeezed out of a 3/8" hard line with a 5/16" return line? I'm currently working with a 408 with a D1SC. I have a -8AN supply line on it now with a 3/8" hard return line, fed by a aero 340lph pump. The system has priming issues and when I get into the throttle it shoots up 15psi and then drops so I need to dig back into the tank and figure out whats wrong. I'm contemplating removing the supply line and moving down to using the two stock hardlines to get back some simplicity and get that stockish look back for inspections.

I realize that -8AN is a must if I want to aim for 1000hp, but I just wanted to see if anyone is running around ~700hp out of either a 3/8" hardline or -6AN flex line?

Thanks!!

700 is not a problem with 3/8" or -6 lines.

700 is not a problem with 3/8" or -6 lines.

Ok great, thanks!!