I have OME on my xj and I wouldn't touch anyone elses crap. OME is vastly superior quality and ride than stock. It'll turn the ride of youre xj into something more like a zj limited. Throw on some 1.5" shackels and spacers in front and you'll wheel like a monster and ride like a cadilac.
other comments
Why the roof rack??? its a frickin station wagon, what do you plan on doing that you need more space? The only roof racks I have seen on xj's are for posing purposes only. Many of the roof racks make a lot of noise at highway speeds.
31's on stock rims will rub like mad without a rear swaybar. Your will also rub a lot on the lower control arm unless you get some special ones.
31's are pushing the gearing on an xj as well. If you have a auto and the 4.0 you might not mind much though.
You'll want and SYE for highway travel if you go higher than 3 ro 3.5 inches (personal oppinion) Thats why OME doesn't make a taller kit. If you use their 2.5 inch kit and 30 9.5's you will have no problems at all with any performance of the vehicle. More than that and you'll either start having lots of problems or have to invest huge money to get it working right. SYE, R&P etc...
You forgot the locker! Open diff rigs are ok for training good wheelers but if thats not the goal its just about posing
In the end, xj's rock. They are an awesome all around platform for wheelin and everything else