3.23 or 3.55?

I have the idea that I am going to build a 400 HP 318 in my '71 Scamp and was trying to decide what gears would be best for my needs. I currently run on a 2.76 gear/741 case in an 8 3/4 rear. It has a 904. Everything is original but not for long. I have seen several sure grip units but do not know which gear will be better suited for what I want to do with it, which is strictly cruising and the occasional 1/4 pass. Can anyone tell me how their set-up's have worked for them?