The off road navigation in the RR is only available on a MKIII Nav computer. I believe the RR Mk III's are locked so you can't (easily) update them to later software versions. You could install a RR Mk III in an X5 and get off road navigation, but most people go the other way as the advantage of a MK IV is much greater than the off road capability (which just allows you to enter way points to go between).