Hey Jeff,
It really all depends on your driving style as to what to use. Alot of the guys are using the 3.73 in 4th -vs- the 3.58 at Charter. I started out with the 3.73 and spin the wheels all the way around the track (see the "spinning my wheels" post on this forum for some info), so I finally broke down and switched to the 3.58...yet to try it at Charter yet, but it was NOT the right gear for Chilton. I bought my 3.58 from Kevin Brill, who just went back up to the 3.73, and you see how well he's doing. I guess, in my inexperienced opinion, do what you're most comfortable with. From talking to alot of different people, the 3.73 is the way to go, but they recommended I go to the 3.58 until I get my driving ability up to the cars ability, then go back to the 3.73.
My 2 cents
Jim