Rear wheel offset is 37.
I did this search for countless hours a couple months ago... 20" aftermarket forged or rotary forged wheels with OEM or slightly more aggressive offsets that will fit stock size Contis. The options are extremely scarce, not only because of the limited width/offsets that fit the X5, but also the 74 hub bore. It seems 22" options are plentiful, but 20" are rare.
If you want to go the custom route, you can talk to Jimmy
Signature Wheel BMW for great prices on custom spec forged rims... definitely NOT anywhere near $10K and outstanding quality (I have Signatures on my M4).
An "off the rack" option I considered was Rohana RF2 which I'm pretty sure come in a 20" and 74 bore with offsets that are very close to stock.
In the end, BMW warrantied my 469M for corrosion and gave me 4 brand new wheels, so I opted to just keep them and save myself a few grand.... mod money which will certainly be spent elsewhere.
