Honestly...how good was the 318...mpg / durability / hp

The only 318 I've ever calculated highway mileage on was my 67 LA in a stripper white hat Coronet 440.
Manual steering, manual brakes, no AC.
It got 22-23, fully loaded on my move from OH to FL. Auto trans, 2.76 7 1/4 rear.
That was the cleanest, smoothest running one I've ever had, but not the most powerful.
Most powerful was that 66 poly.