C63 is a regular entry level luxury car with a big engine in it. The M3 on the other hand has a lot in common with super cars on the other hand, and I say that as someone who'd worked desining cars. The M design team simply do some very high quality upgrades to the regular 3 that puts it in a different class. AMG on the other hand call it in.
Don't get me wrong the results with the AMG are good but the AMG is just a badge and an engine, the M3 is the real deal.
Clean cars are happy cars!