Gas mileage 225 Slant 6

I’m curious then,what would a 273,a 318 and a 360 with torqueflite get if driven normally? I’ve heard others say the V8’s do quite well if you keep your foot out of them
I had a 71 Dart with a mild 360, 904 and 3.23 gears bump 20-22 when I drove like an old man, which wasn't often.