I guess if you're more into extremely expensive drag racing, go for the C63. Arguably too much power for that platform for spirited switchbacks (LOL at that video "oh shit! not good!" as he almost loses it), autox, or even regular track days.
But it seems everyone around here wants more power. To each their own! Me, I like the balance of the M3 (each generation), seems to have the right amount of power. Anyway enjoy your merc.