They no longer use the straight six in the Jeep Sahara so I would deffinately say to go with the G8. The Jeep used to be a good product but stupid chrysler is trying to go cheap on everything and they discontinued the 4.0L straight six because "It wasn't cost efficient" and "It wasn't 'enviromentally' friendly". Which translates too, how else can we degrate this once great off-road marvel, and, How can we make it seem like we are doing it for reasons other than our own pocket books. I hate modern chrysler if you can't tell.
The G8 is a solid car, whether they choose the six or they go with one of the eights, they are all strong reliable and they will all be a much more comfortable car than a sahara will be. Plus figure things this way, less cost later on down the road when it comes to the 4x4 components. If they aren't going to use them, why pay for them?