So, I've just swapped a Maser GT 4.7 Auto for a C63 Estate. I did it mainly for practical reasons and needed to release some cash.
The C63 is a very good car - not sure how it stacks up against the S65 - some of the AMGs went for all out power rather than handling so you need to watch that. The C63 handles very well and the engine is just amazing. I have no regrets as it is a circumstance thing for me.
However, it does not feel as special as the Maser. For a start, nothing compares to the Noise the Maser makes, even in non-sport mode. That has a significant effect on how you feel driving. Then there is the way the Maser makes you feel...
Basically, the AMG is good. Really good in fact. It is hard to think of how one could make a "better" car. However ,when circumstances dictate, I will be straight back into a Maser (GT or QPIV).