My idea is to lift what you need for what size tires you have. In your case you want to add 1.75" spacers to lift the xj a little bit higher - why ? so you can run bigger tires. If you were to run 31" tires, 3" of lift is a good starting point, see if you NEED the 1.75" spacers to clear 31" tires better. Do you want to run 33" ? put them on, and see if you need the spacers or not. Before going 33", you might want to see if you gearing is suitable for that size tire. Also, have you thought about shocks ? Another thought is less lift is better - the higher lift, you will lose low center of gravity, making your XJ more tipsy.
The super swamper ltb's look nice - however I hear they wear pretty quickly - maybe thats why their pretty cheap. For a daily or a XJ that sees the road often, I'd say no to LTB's. I have the super swamper MT's on my XJ and are Great on the road.
