No, it's not a direct rival to the M5 and RS6, but Mercedes is democratizing the fast wagon (sort of) bringing this E53 ...

This is precisely what it did with the original E53 X5 Le Mans prototype ... V12 engine from the Le Mans-winning V12 LMR and served as a precursor to the BMW X5 M, one of the first high ...

Although the BMW 550e and AMG E53 Hybrid use similar PHEV powertrains, they have totally unique personalities. It's wild to think how advanced, capable and efficient both of these vehicles are.