Good explanation. Another thing to add is that the size doesn't indicate how much air the carb flows. 32/36, 38, or 42 is just the size of the throttle bore. What's more telling is the venturi size. The sidedrafts are advertised with certain sizes ("42s" will widely vary in venturi size). The downdraft Weber/Holley also can have different size venturis, but not always advertised as such. A stock 1200 probably works best with smaller venturis, a racing 1200 would like bigger venturis. If they are too big, the fuel economy and low-speed hp can suffer.