My 65 Mustang, when I drive it carefully, can reach around 26-27 MPG on the highway. Our old 99 mustang (greywolfs mustang now) could get around 28MPG on the highway with the 3.8L V-6. My Volvos with a 2.3L turbocharged 5 cylinder can get around 29 MPG on the highway if I keep off the gas, but those cars weight in around 3400 lbs versus the mustangs 2700.
The advantage of fuel injection is not cut and dry. A well tuned carb'd engine can reach the same economy standards. However, the carb can not easily adjust to changes in barometric pressure and temperature which impact the density of the intake air. Carbs are generally tuned for a certain operating condition, so others may not perform at max efficiency. A large jetted carb can be great at WOT for efficiency, but will suffer cruising around town and vice versa. And EFI car can adjust for various conditions better than a carb, unless you wanted to rejet your carb every month for the weather conditions (or get a holley with the adjustable jetting block).
I personally think the real driver for EFI has been reliability. At least once a year I'm retuning the carb a little. Every few years I rebuild the carb. And thats on a car I only drive between 5-8k miles per year. Since I've own my 91 explorer (bought in 1995) I have never had to touch the EFI system outside replacing the fuel pump because the output and inlet lines on top rotted out. Sure, it could probably use new injectors, but it still purrs like a kitten, starts up on cold mornings and hot afternoons without a hitch. Same with my volvos. Still have not touched the EFI system, other than replacing one O2 sensor. People these days are less inclined (or able) to tinker on cars. They expect that when they turn the key it should start up with no hassles. No pumping gas pedals, no messing with chokes.
The emissions on a carb'd engine are no better or worse than an EFI car. I had my 65 tested once. Didn't have to be tested, but I had to have the inspection for the state I was in. The guy asked if I wanted it and told him I didn't think I needed it. He said that I didn't, but I was paying for it anyways. So I had him do it. I compared it to the 99 mustang with the 3.8L in it. The emissions were almost the same, even with the Catalytic converter.
But then again, take a carb'd car to a young dealer mechanic and they'll looked confused as hell when they can't hook up a computer and they'll say "oh, I can't trouble shoot without the computer hook up." Been there...done that.