I bought my Range Rover 4.6 HSE with a bit under 61,000 miles on it, now at 66,000 and it needs a good sum of minor repairs on it (see other posting).
What Land Rover you go with is a personal choice. If you get a Range Rover, I would absolutely get a 4.6 HSE. The 4.6 is better than the 4.0 motor, not to mention more powerful. These trucks need all the power they can get.
I would be more concerned with the maintenance than the mileage on it. My truck was not maintained... at all. As a result, it's got a bunch of small problems. The oil gets black after about 1000 miles, so I'm doing a lot of oil changes now to clean the engine out.
If you get something with well over 100,000 miles, it probably has a lot of new parts in it and is ready to go another 100,000 miles.