i see were your going with this...
haveing a 3/8 line charged @ 12psi will flow less then a 1/2" line with came charge if the valve open time is the same
pluss the bigger line has more fluid wantitng to go through the said hole
weather or not it make more power or not... it does make current power level easier...
Wait.
The fuel flow is dictated only by the RPM of the CP3's when the truck is sitting still. Flow itself does not change unless you are starving the pump and drawing against a vacuum. At low throttle, 90% of the fuel goes back into the tank, and 10% goes into the rails. At high throttle, 90% goes into the rails, and 10% goes back into the tank. But the supply flow doesn't change.
What is important is pressure. When we launch these trucks, you must push the fuel "uphill" against acceleration. If you don't have enough "push" you start to draw against a vacuum and decrease flow.
Now, which one weighs more? A column of fuel 6' high that is 3/8" dia, or one that is 3/4" dia? It takes a bigger pump to resist the acceleration force if the fuel weight is higher.