[bobcowan]

3/8" (-6) will fed up to about 500'ish hp with a pusher electric pump. A puller mechanical pump will have some trouble feeding more than 500hp with those lines.

With 600+hp, I would definatly move up to 1/2" (-8).

3/8" fittings on the fuel pump will cause some restrictions. I would be concerned about that. You're running two pumps - does that mean you have two pick ups? If so, run -6 from each pick up to the pump. Then -6 out of the pump to a manifold that's -6x2 in, and -8 x 1 out. That should maintain full flow.

If there's only one pick up, I can't see a reason to run two pumps in series. Replace those two with a single high flow pump with -10 fittings. Like Aeromotive A1000 with the proper pressure regulater.

To make life easy, use braided hose from stem to stern. A little more expensive, but it sure is easy to run. You can have the whole thing done in a day.