Yeah, if you were going for prestige I think a c63 or something would be more practical and still fast.
I don't buy the chassis story, plenty of people making massive power in jap/American/Aussie cars and the chassis' hold up fine. But if they meant the car/chassis couldn't effectively put any more power to the ground or it'd be undrivable I'd believe that. If not id say its just been detuned so the engine or drive train doesn't grenade itself.
People in america have made ~1k HP on the old sl55s with intake, exhaust, new turbo and a tune. I think the shop that did that can also get massive gains with a tune alone. But either way is probably a bad idea since I don't think they were very reliable even in stock tune!