I understand what you are saying about needing more air to produce the same power. Problem is, the only way to pull in more air is more displacement. There is nothing I can do to make a 318 engine pull in more than 318 cubic inches of air per combustion cycle. Obviously changes to cams and valves impact the exact airflow in and out of the engine, but the maximum amount of air still cannot exceed displacement on a naturally aspirated engine.
We actually pull in the same volume of air in Colorado as they would in Florida - the air just has less density. That is the reality we have to live with at altitude. So we make intakes as free flowing as possible, but we have to live with the fact that our air has less energy in it. And if we oversize a carburetor, the lower density only compounds the issue of poor signal at the boosters. Thinner air passing through the venturis has less vacuum than denser air. This is even higher than the standard air energy loss. We lose approximately 16.8% vacuum pressure at 5K feet. This means the problem of an oversized carb will only be compounded at our altitude. I think your original advice is pretty solid.
