I have exactly the same wear on my N62B44 on No-8, I can see it from below when I had the sump off for a gasket change

I would say 99.9% this is due to overheating, mine has been overheated on at least 2 known occasions, the previous owner left it running on his drive and found out the electric cooling fan had given up, the tell tale sign was steam coming through the bonnet vents!!

I bought the car with several known faults, it has covered well over 50,000 miles since it developed piston slap because the bore/piston are so worn, it runs on 10W60 and hardly uses any oil, if I run it on 5W40 it smokes like crazy

Im sure ive read about your car on one of the facebook groups, im also doing a Z3 V8 but with an M62, do you have a more detailed write up on it? Would love to read more