3.73 or 4.88 ?

That statement is really KEY to making the correct decision.

The following fully applies to those operating a D20 transfer case or the D18 without an O.D.
As you know the axles reduction ratio is refered to as the final drive (F.D.) ratio.
With the addition of O.D. the vehicle has a compound F.D.
Example 5.375 x .75 = 4.03 compound F.D. or 4.89 x .75 = 3.67 compound F.D.

For road useage virtually no one will be fully content with a jeep having final drive gears lower (slower) than 4.27.
That said few if any extreme off-road jeeps will have F.D. gears higher than 4.09.

This implies that a jeep with 3.73 or higher gears will make a great street jeep that's just not capable of extreme off road use.

I.M.H.O. 4.89 F.D. x .75 O.D. provides the true middle ground for the best of both worlds.
That said I recommend gears no higher than 4.03 compound F.D. for Hurricane powered jeeps.
See: http://z4.invisionfree.com/CJ3B_Bulletin_Board/index.php?showtopic=4538