FWIW, a small pipe (like a galvanized one full of rust) has nothing to do with static pressure. If you measured it, it would be the same as if it were a fire hose. But, it does affect the flow rate, which is what you notice. With the potential for earthquakes, I'd prefer something that is a bit more flexible than rigid copper. But, then, I'm not a plumber, nor from the Bay Area.