Shocking you were able to fit 245/35-20 & 285/30-20 on W212. I mean its 26.8" diameter tires. That would be about the max one can run on C219 CLS and R230 SL (both of which have a lot more room than W212).
What offsets? Any fender modifications? I see you're using non-stock body kit, hence the question.
little modification on the front bowl (bowl-like metal supporting the shock absorber) for the tyre not to rub
the rear clears up barely as the body is straight in-line with the outer surface of the wheel, i haven't even had the time to drop the height. let you know later, but the workshop said it would clear up just fine.
if you are buying forged, just console with the engineering/shop.
regarding the offset, please just contact showroom-motorsport. it's not that i am promoting, it is just that they take care of mine just fine...
10.5 i would say is the max. i've seen a friend of mine go with 11", and it is petroding out of the body.