The main question is, what are you going to do with the Jeep - are you going to stay on the highway, or do some offroading.
I had 31st on mine (05 as well), and it did fine on the road, and was able to wheel pretty well offroad, but the tires were a bit too big (they will stuff up in the wheel wells, and eventually take off your fender flares).
I'd say if you are never going offroad, then you could probably do a 32" tire. If you are going offroad, then 30 will probably be it.
You should look into a 2" spacer lift (if you change your mind). It's pretty much just a spacer, or shim that lifts your Jeep up a bit, but doesn't change the way it rides, or the stock suspension.