PG will give you the most mpg, less hp to turn. 350 will give you more than a 400 also. 400 is the strongest, probably will never break it. Of course, I am a little biased, I have been running 400's since 1980 except for a few months in 85 when I had a 66 Chevy 1/2 ton with a 350/PG combo. Man, those were the days.