I get your point, but you talk like the number of cylinders means something. A turbo ecotec 4cyl can very easily make serious power. And the ecotec is much better supported by a much cheaper aftermarket than any Mercedes.

If you are a performance nut the GXP Solstice & Sky are great platforms. Now if you want to argue stock performance... then you really aren't a performance nut. So buy whichever one comes in a cooler color.