I have a 2 piece hard top.

The hard top won't do much good in a roll over, it's only fiberglass. I saw a 199? 2 door Tracker/Sidekick in a junk yard that had rolled. The center bar was bent about 20 degrees to the Passenger side, the window frames on the doors were bent as well. Driver's side hood and front fender were pretty damaged as well. It looked like it came to rest on the driver's fender and the center bar. I also have reason to believe this was a low speed, snowy road induced roll (we live in Utah). I wouldn't count on the center bar to protect you in a serious situation, the metal is just too light. Rear seat passengers have no protection at all.