its this simple
do you want crisp fast throttle response? or do you want it to hesitate and have slow throttle response?
if you want it crisp a 600CFM carb with vac secondarys is the way to go and youll get better fuel economy.
if you want it to hesitate its a 650-670cfm carb
im running an 850 Mec Sec DB on a 496 thats almost 2 times the size of your motor so you do the math a 600 is the ticket here all day everyday!