you want as big as you can utilize, if you go too big your car will get too much air and die basically.
same problem i'm facing with my car, couldn't afford a new carb at the moment, so i put a 1000cfm carb on it lol, when i stab the throttle to go wot it stumbles then comes up in rpm. not sure how much its costing me but i can't cut a lite for **** like this
just a slow n/a mustang
fastest 1/8 mile 6.10s @ 113mph 330ft 3.92s 60ft 1.36s