I have been running Pro Circuit pipes since having a stock motor to a ported 4 mill and it has always had plenty of low end grunt for the trails as well as giving me enough top end to have fun on the drag strip. In my opinion, I think you will like the Pro Circuits. My buddy has FMF's on a stock motor and doesn't like where the power band is. I am no expert by any means, but I can tell you I have been more than happy with the Pro Circuits. The only way I would consider changing pipes is if I was going to be spending more time on the strip and wanted more top end.
I have an 89 and it is a J Arm bike. If your not doing a lot of jumping, I think the J Arms add character. You can always beef them up with a set from Stellar in the future. 89 doesn't have a key or brake light, but that can be added easily.