In my experience many sellers assume X5 and X6 wheels are all fully interchangeable, whereas we know they're not.
I'll probably use off the shelf 72.6 /15mm spacers on the rear with spigot rings on the wheels. I'm also waiting on a confirmed quote to make one piece spacers with spigots to allow the 74.1 wheels to fit the 72.6 hub. Estimated cost circa £60, so not vastly more cost. I have to measure the hubs carefully when I return to the UK.
It occurs to me it could be wasted effort and expense with milder winters for the foreseeable. But I already have the BMW approved winter tyres and 3 of 4 wheels.
I concluded the 285 tyre on the 11" rear rim though OK just doesn't look quite right. When the second set of type 300 rims are freed up I'll buy some all season rubber which in time will be all I am likely to need