I've been revisiting the topic. I asked BMW and they quote me £2900 for 4 19" wheels with tyres. They do look a bit meh!
However shopping around I can have 4 x non-oem 20" wheels with all weather for ~£1900 ... Reasonably close to the BMW looks.
https://www.wheelbasealloys.com/allo...ear/bmw/x5/go5
Also in 21's but with a lot less choices of tyres/wheels, but these were are 'ok' but £2600 with the all weather tyres:
https://www.wheelbasealloys.com/allo...nch/bmw/x5/go5
Anyone took the plunge yet? What did you buy?