Take it from "The HiLift King" /forums/images/graemlins/grin.gif,get a 60".I have a 6" lift and 37s and the 60" is plenty tall,even without chaining the axle up.
With a 6"susp. and 35s on my K5,my 48" was too short.On pavement it was fine but off road in different situations is where I would go all the way to the top and still need more.