Blown- I apologize if that came off as smart, in all seriousness, I did not mean it that way, my point was just that with a carb, you have no exact idea what its going to do in any given transient state. Yes, you can monitor what it does with a wideband, but that is very, very different than knowing what it will do with certainty in advance.
In the operational state that I mentioned above, with an efi system, you know with certainty that in closed loop the engine will get the correct amount of fuel for a stoich burn, plus or minus some small amount.
Circling back to efficiency, this means that when you aren't getting on it the computer is constanly providing just enough, but not too much fuel... And it is checking and correcting itself many times each second.
In the same situation, a carb is adding fuel based on any number of mechanical controls you have tuned it with. While they can certainly be tuned to be optimal for many individual states of operation, in fact for many states, they will not be optimally for all.
D- I will not argue with your own experience as regards mileage on your vehicles. And while there certainly have been inefficient efi systems (alpha n, batch fire, most tbi), I still maintain that if you take an engine with a properly tuned, modern, multi point, sequential fire efi system and compare real world day in day out mileage against the same engine in the same vehicle, but with a carb, any carb you want, the efi system will win every time.
Back to our cars and our cobbled fueling together systems. I will grant you D that you can probably tune a carb that will be 80 to 90 as efficient as well tuned efi system. My point is, and has been, that for us hobbists that don't daily drive our cars, mileage doesn't really matter. Most of us lose more fuel to diurinal evaporation than to poorly tuned fuel systems.
For me specifically, my beef with my EEC based system is the weight and the cost. For the cost of everything I bought to get the system working (and I did 100% of the work), I could have had a 347 with nice alum heads, a great carb, and be 75 pounds lighter than I am today.
As is, I have a mild engine that gets great mileage and is much heavier than I would like for what I do with it.
OP - my point in posting all of my posts was to give you a different point of view on putting in an efi system, I am sure with all the posts and differing points of view, you will be able to make the best decision for you and your car.