The primary throttle bores/venturis in a small 4-bbl will more than likely be smaller than the throttle bores/venturis in a 2-bbl carb, leading to crisper throttle response and better gas mileage, provided of course, that you keep your foot out of the secondaries. With the 4-bbl, you'll have a little additional power for passing or other demands over the 2-bbl.