I change the 4 tyres at 23.000 KILOMETERS.
Of course the front tyres were not -aparently- to change, but in this kind of car you NEED to change the 4 at the same time. Otherwise the car becomes very nervous.
Before my actual M5 I had an Euro M3 (321 hp). I changed only rear tyres, and I only had to wait one day to discover that I SHOULD change the front ones.
It doesn´t worth to keep the front ones. What is an M5 if you can´t enjoy it completely.
Haven´t change disk brakes yet, (actually 31.000 Km). Seems that break pads will be change in next INSPECTION I, at about 35.000 Kms.
José L.