That a good question. Haven't figured that out yet. Just with portal axles alone with no lift I can run 38's on the JK with no rubbing. And due to the very low gearing I'd have to run around that tire size if I ever planned on driving it on the highway. Right now the lowest gear ratio they have for the axles themselves is 4.10's. However they will have 3.73's here soon which will allow for lower rpm's for higher speeds.
I really didn't want to sink a bunch of money into the XK due to the higher mileage. By next summer I'll be somewhere around 165,000 plus miles.
That would be sick but not sure how long the 4.7 is going to last in the XK. I can already use a new transfer case or a rebuild and I'm sure the transmission will be getting to that point by the time I get the money to do what I have planned. This isn't something that would happen overnight due to the cost. I was planning on getting the JK and having it paid off within the first 2-3 years then go from there.
I'd have to look into it and see if they make a portal kit that a direct bolt on to our rear axles to even consider doing it to the XK