MyWay,

There are two carb restrictions in the SSC rules. First you must run the carburetor that the manufacturer supplies with the engine. Second you cannot modify the carburetor in any way which precludes drilling it out. Now on to your observation abour performance and carb throat dimension -

The engine with the biggest bore will have the most performance if a couple of criteria are met:
1. The fuel system is able to supply all the fuel that the engine can take - a pressure bladder is necessary with large bores
2. The timing of the engine is such that it can get the fuel volume in and out of the combustion chamber

The larger the carb bore (generally) the less vacuum is created for fuel draw, hence the need for a pressure feed system. Tuned exhaust are not legal in SSC but in Open A a tuned mousse can exhaust system will help get more fuel and burned fuel out of the engine. These two changes are likely to have more impact than the throat diameter of the carburetor. Just my $.02 worth.