The axle gears, you'll wanna a 33"-35" for the 5.38s... depending on what your orginal tires size/gear ratio was. But less than a 33", you may be turning some high rpms on the highway.

the 307 kit, it doens't matter what tire size since they only come into play offroad. basically there will be benefit at any level. maybe slightly more benefit for the larger tire guys becuase its that much more difficult not to slip a little clutch when on a steep hill. Tera's will keep you from rolling back and having to dump the clutch to get going.

-Rob