Great write up on the RRS, I have to admit I do like the model you have but I hated the one before that due to the low rent interior.
Now that jag is awesome, I have a real soft spot for the XJ and that I interior is stunning. But it would be very hard to choose between them, the 4x4 feeling is hard to move away from. It brings you back down to the same level (height) as everyone else and that's something I think you would miss (I know I would). I think the RRS and the XK give you the balance, just a shame they both drink fuel..
I have a feeling that I am going to feel the same way about fuel, going from a 2.0 Tdi TT to a 3.0d X6 will be a bit of a shock