I have a 97 Cobra, the headlamps were looking like ass. Used 2000 grit, kept it wet. Had to get aggressive, took a while, then used my buffer with wool pad at 1000 rpm and some polishing compound. Looks great, only thing is driver side has moisture behind it, so will have to get new one anyway.....damnit. If it hadn't been for that, they would be brand new looking. Wish I had a digital camera, would have taken before/ after pictures.
On a Grand Cherokee the other day, I started with 1000 grit to get the worst of it off, then went to 2000 grit, then polish. Turned out pretty well also for as bad as they were.