Not only the size of the pickup but the sock that goes over the end to keep lumps out of the fuel system can restrict flow. I was suffering from fuel starvation a couple years back. Very frustrating, and embarrassing, when doing a burnout leaving the ferry boat on the way down to a car show and having the car sputter to a stop. Not only was the sock on the pickup restricting flow but it was also disintegrating and the particles of mesh caught up in my fuel pump. Managed to get to the show and home but had to behave myself driving. I put an open 1/2" pickup in the tank and installed a large filter in the fuel line right where it comes out of the tank. I took the pump apart and cleaned the valves but it was never rights so I had to buy a new one.