Generally speaking, the EFI will be more efficient because it is more accurate. A carb has three fuel metering circuits, and the mixture can be adjusted to be pretty darned close in most situations. EFI has dozens of fuel metering points for all kinds of situations. Assuming the same amount of care is given to both tunes (carb and EFI), the more accurate system will be the most efficient.
Efficiency not only save gas, it makes more power. The peak numbers will probably be the same - or real close to it. But the torque curve will be flatter, and the area under the curve will be greater.
Anything with individual runner intakes - carb or EFI - does better with a cam that has a wide LSA, like 114-115*. The narrow LSA tends to cause some reversion as the intake valve closes - there's no common plenum. And then fuel get's pushed back up into the stacks - the famous weber fuel cloud.
Carbs of any kind require a good vacuum signal. And if the intake charge velocity slows down enough, the fuel will fall out of suspension, and become a liquid at the bottom of the intake port. Especially with the individual runners of a weber carb system.
The nice thing about EFI is that's it's not dependant on a solid vacuum signal to feed the cylinders. The fuel is forced under presssure into the chamber regardless of air flow.
I run a huge roller cam, just about the biggest off the shelf cam I could find: 304/314*, .608/.608", 114* LSA. The car is just a joy to drive. It idles very nicely at 850 rpms, with just enough of a rumble to make you smile, but still allow you to keep your kidneys and your fillings. It will cruise all day long at 2,000 rpm's, and get 18-20mpg. The exhaust note is very pleasant around town and while cruising.
But mash on the gas.........
