4.56 gears 4-speed?

If im seeing the correctly you are currently running a 456 gear with an auto trans ? If this is the case then the 4 speed will be better because 4 gear will be a true 1 to 1 ratio, your auto trans torque convertor never sees true lock up so the the cruising rpm will be higher with an auto trans . If you do use it alot on the highway , 456 is a big gear , but for local cruising its fine , I run a 430 with a 28 inch tire and turn 3200 rpm at highway speed .