Okay, here is what I have found out so far. Please, anyone who has requisite knowledge on any of these numbers please pipe in. None of us need any rumor-ville because believe me, the Aussie community has that part covered on the X5 wheel set up. Anywho, these are the numbers I have found to be confirmed by LR and BMW peeps and if anyone has documentation on any of these numbers to confirm or debunk, please post it here.
Load Rating for the Disco 3 17" and 18" wheels are 940kg and the E53 X5 wheels are said to be 900kg to 1030kg (Apparently depends on who made them). The E53 X5 wheel is the only one that meets the load rating or similar to the Disco 3/4; all other BMW are for cars or are too wide like for the performance X version SUVs with the super fatties on the back. So the 900kg would be slightly less than the max loading of 940kg of the factory LR wheels; a decision that only YOU can make if the drop in loading rating meets your safety margin. The thing that sucks is the BMW wheels are not stamped on the inside so the only way to confirm is to know it is a genuine BMW wheel that came from the factory as apparently there are Chinese knock-offs for replacement wheels. I confirmed from the seller of my wheels, that they happily replaced their factory off the showroom floor wheels with 20'' blings so I think I am safe. Honestly, if you buy a set, you are probably safe. For reference, the information I found is that the 20" RRS wheels are only rated at 858kg (I say only, but that is a pretty heavy per corner) regardless I think the Disco 3/4 is fatter anyway. Just a comparison.
There is one guy who's been running these X5 wheels now for 40,000km with zero issues and a few others with less mileage. I am guessing they are much higher in mileage by now since many of these posts started in 2012 and 2013. What I have confirmed is that nobody has openly disclosed any issue with the wheel fitment or failures of any kind; not saying it hasn't happened, saying I have not found any failure documentation. What I have found is everyone is having tire fitment issues because like us here, everyone seems to want to stuff as much rubber under their wheel-wells as possible and this is leading to the same issues we see here.
For me, this tire size will not be an issue. 245/70r17 and and 265/70r17 are very popular sizes with zero issue and exactly where I want to be. I am running a near perfect size on KM2's for my uses on my LR 17" and the X5 wheels will be no different with KO2 (have not researched exact size yet). Bottom line, stay at or under a 32" tire or you will have to cut and carve and do all the modifications we are familiar with for large tire diameters. Keep in mind, these are 7" wide wheels, the same as the 17" LR wheel and that means a 265 is about the maximum width from the sizes I've seen.
The lugs nuts are confirmed below for the folks who have been running the X5 wheels. 14mm x 1.5 and 60 degree conical lug, torqued to the same spec as LR (LR and BMW same for these wheels). It appears this Gorilla lug (link below) is very popular so I am going to research the specs, and then see if I can find one that will accept my current socket size, and is NOT chrome. Many people have complained that the below linked lugs rust, but the fit is what is required and apparently there was not much on this size to choose from. Again, I will continue to research this and most likely order a set for one wheel to take some torque, alignment, and thread specs. The lug change is specifically needed due to the thickness and offset of the X5 wheel. According to the safety nuts in the Aussie government, they are inspected for changing to V6 brakes on annual safety inspections and the lugs have to meet a specific thread lockup count (probably similar to many stateside gov inspections we see in some states for modifications). Personally, I don't disagree that the lug nuts should grip as many threads as possible so it is about turns on the lug, how many threads are mated to the lug. Another option is to put longer studs in the hubs, an option I am not willing to explore just yet since it does not seem to be the only option since lugs are available.
Sorry for the long winded response, just trying to paraphrase the information I have found thus far. So far, I am happy with what I have found. Time to start shopping for lug nuts!
Gorilla Nuts
Oh, and the BMW center caps.......I guess the LR cap won't fit in there I think I can manage to plastic-dip those and be happy! hahahaa, you wouldn't believe the drama about the center caps! phew. All and all, I joke, but it's a really good thread on these wheels.