Today, dollar for dollar, is the 318 faster than the 340 ???

Maybe so, but do you travel across the state on 3.90’s or higher? You built the box, I’m trying to stay in it.
My gearing in my cars start at 2.76 and go to 4.30's. However, couple years ago we went through 9 states with 3.55's in a full time 4x4. I avoid interstates if I can with the oldies. Pay attention... you'll learn that I like highway gears.