Not 100% sure...........
My pump runs right at 4.8 and I do not have any issues at all. Ages ago I had a 10 PSI pump and regulator and could tell no difference between 1 PSI and 9 PSI. That said, I would be a bit worried about leakage past the needle valve, especially at low speeds. If it were me, I would find a pump in the 3-5 PSI range for peace of mind. Meanwhile, if the engine starts to bog at low throttle settings that will be a sign you are getting too much gas. Our carbs really are not demanding for pressure, we use maybe a gallon an hour at most.