Putting in a larger carb than needed will only hurt power. 650 is good from 302 to a mild 331, 750 is for a mild 331-351, 850 or more your looking at 400+cid. I am no expert though, but I know that carbes use the venturi's to create velosity, therefore going larger than needed will result in lower velosity and if the volume of the smaller carb is never needed, then it will result in lower power. People often overcarb thier engines just like they overcam them. If you put in a part that operates in a range your motor is not capable of operating, then it is just a waste.