How did you run your fuel return line to fuel cell?

So I've been wondering why run -6 from the regulator to the carb and not just run -8 if the rest of the line is -8? Right now I'm running a Holley 950 HP that will eventually be converted to E85 and the guys at aeromotive said I definitely need a bypass regulator for that flow. So I too am curious as to how anyone has run the return line and what's the reasoning for the -6 to the carb. My whole fuel setup is wrong and I'm changing everything so I want to make sure I'm doing this right.