No opinion on the Touareg v X5.
For me, Form follows Function. This weird "big rim" design trend is like the 1950s and the taillight fins...one company did it, the public liked it, so they got bigger and bigger- the public then believes it must be like this to look good.
If you are driving a race car and need room for bigger brakes, you trade off rotor size for expected road surface, and engineer accordingly...but just putting bigger rims on the wheel for some kind of 'look' is poseur. To me. Give me a light, strong, true wheel, with decent sidewall, and I can outdrive those 'muscular and sporty' looking cars running on rubber bands.
Folks get low profile tires
on big rims and note a 'darty' and 'direct' connection to the road....but rip through a back country secondary road, with paving irregularities, with constant weight transfers side to side, and you'll understand why low profile tires
CAN be a significant downgrade. Lower profile tires
will dance off the surface as the contact patch is poorly controlled, and that connection that felt good on the test drive has vanished at speed.
Now, where does one draw the performance line on the X5, dunno. 18? 19? 20? . But I do know the brake rotors are all the same.