That's what I was wondering too in another post the other day. Cruisers I know run with a stock caster of around 3 degrees, why is it then that our XJ's need 6-7? I'm currently at nearly 6" still with a LP D30 - cut and turning the D30 is definately a lot easier than swopping in a HP D44. I've been down that road and just couldn't justify all the related mods for my simple DD.
My suggestion would be to check the slip joint of your front propshaft and just do the cut and turn - I'd love to hear how it turned out. From the little research I've done so far the stock relationship between caster and pinion is about 11-12 degrees. If you're going to cut and turn you could go as far a moving that relationship out by about 4 degrees to say 16. You do however have to realised that when setting it up to be perfect at 6" lift, there is no going back, you can't lower it again unless you'll cut and turn again. What I would do it to set it up to be perfect for say a 4.5" lift and then compromise a little while running 6", knowing that you can go down if you want...seeing that there is a lot of focus recently on low centre of gravity lifts with a bit of trimming.