Hi Carlos,
Have you heard from the guy who's got the 21"rims?
Meanwhile,I have been doing some research and have found that the 7-series 760Li uses these according to realoem.com data.
These are style 128 and as you said in your first post,these are 21x9 and 21x10.

The rear wheel has an offset of 25 which is ok and will fit your X5 nicely ,some 30mm further out than oem 19"s but still not flush with the body!

Now,the front has an offset of 20 and is more complicated!This wheel will stick out 33mm more than than 19" and even slightly more (2.6mm) than a oem 20".Still,I am looking at my front 20"s and they are into the body,so an extra 2.6mm will be fine.

I have done these calculations assuming that you will be fitting tyres which match closely the 19" oem rolling diametre.
The recommended tyres are 265/40 front and 305/35 rear.(just 0.8% over).

http://www.realoem.com/bmw/showparts...71&hg=36&fg=15