Fuel restriction w/ 6an line?

If you are referring to the friction losses causing pressure drop that will occur in any hose/piping when moving a fluid, I agree there will be some. There will be in that honking #10 feed line. It occurs in just about EVERY case, much like voltage drop in electrical lines.

Colebrook Equation, Reynolds Number, D’Arcy-Weisbach Friction Coefficient whichever you want to use it's going to happen.

IIRC, the drop in a system like this with short runs, low fluid movement rates and pressures will be so small that it would undetectable without some precise measuring systems, not some 1.5" fuel pressure gauge. You're likely talking .05 psi or less in most cases. Maybe you could figure out the actual pressure drop to educate everyone.

Totally insignificant in the big picture. Making mountains out of molehills