electric fuel pump

I am going to put an electric fuel pump on my 65 Barracuda Furmula S. The car has a stock 273 with a 4 barrell. When I was looking at them I see there there are more than 1 options. 1 options is 2.5to 4.5 pounds and the other is 5 to 9 pounds pressure. Which one should I go with?
Thanks