Which to install 391 rearend gear or lower?

I have 4.10,s in aa 4 speed car and 391,s in my auto car,both cars have tall 15,s on the rear.I don,t do alot of hwy driving,but I would suggest 3.55,s for abit of performance on the street/track.If 75% of hwy driving?go with the 3.23.s.