non a body slant six d100 question

A few years back, my daily driver was a 76 D100 2wd longbed with a slant and a 727. Since I generally drive too fast, I coulda replaced the throttle with a toggle switch, lol. After a year of this, I put a mild 318 (headers, 360 cam, BIG TQ) and fresh 727 in the truck and actually GAINED 2 MPG!
If you have a very light foot, I suppose you could save a little gas with the six. But if you are hoofin it right to it, that 318 don't need to work near as hard as the six to get ya down the road. Just my 2c.