My post was half uneducated and half unclear
I agree with the stuff about MPG and camshaft choice. With older engines and technology especially, you need more fuel to make more power (as a general statement) and more aggressive cams mull in more air and fuel (inefficiently). My question was actually what 82SC meant by bad mileage (I personally don't car until it gets below about 15).
I showed my ignorance with the comment on different camshafts in different engines. What you say makes sense - a 911S cam in a bigger engine probably feels less peaky because the bigger engine is more torquey 'cause it is... bigger.