The only real differance between the two is the ECMs control of the ignition timing.
Not true at all. While the ECM can also control ignition far more accurately and in better ways than a mechanical distributor, and do it in harmony with the fuel - it's how it can control fuel in ways a carb simply can't that sets it apart.
Best way to go EFI is either factory with a few minor tweeks or best is to go with aftermarket that uses a wide band oxy sensor.
Agreed, although a bit more than minor tweaks, especially if the system was tuned at 14.7:1 for catalytic converters. 14.7 is neither powerful nor fuel efficient and is only to make the cats work right. In either case, a WBO2 sensor will yield the greatest gains in both power and MPG. Yes, factory ECMs can be programmed to add WBO2, or the WBO2 controller is programmed to output to the narrowband ECM input in a way that is more accurate for the factory ECM to use.
Car I am driving right now got 20 MPG hIGHWAY same engine with carbs gets 24.
I call BS - or it's a crappy mismatched setup like Victor race EFI manifold on a street engine - or it's a non-programmable EFI - or you need to let me tune that thing for you.
I'm not trying to start a war here, but I have never seen a carb setup turn both
the same HP and the same MPG as tuned EFI. You're the first. I've seen a few come close. Yes, they can be mis-tuned with the wrong settings (such as an overly sensitive accel enrichment, squirting extra fuel sporadically), but then that's another case of mis-tuning. Or, like above, mismatched parts like a hot 347 with a stock 5.0L HO intake setup choking it. But apples to apples - no.