3.23 gears and speedo cable

Sorry, yes its an 8.75/489 housing.How much different would the 3.55 be compared to 3.91? Doesnt sound like alot, could i atleast run 60 for a long period of hiway without stressing the engine and trans? Not looking to make it a hot rod/street racer, just want to cruise around, take weekend trips somewhere every now and then. Is that your `cuda? what gears are you running?