I think the 4.88 v 4.56 is a matter of how much you intend to take her off road. My jeep is for weekends, bad weather, and whenever I feel like it. The only time I'm above 70 with her any more is on the way to drive her off road in PA. That being ssaid, I'm perfectly comfortable with my 4.88s at 70mph. I don't feel the RPMs are too high and crusing is a breeze. The low-end crawling benefits of 4.88s with the MT are great. Very low crawl ratio.

If I had the turbo before the gears...I may have gone 4.56, its hard to say. I'm with ross that if you DD your vehicle and spend a lot of time on the highway at 75mph then 4.56 may be the better choice. Gears are a leap...you really just have to read enough about them to make a decision you are comfortable with. Either way, I think the only mistake would be to spend the money on something like 4.10s. You'd be happy 4.56 or 4.88.