You should be able to run mid to low 14s in the C43. Remember also that the C43 and C36 are exactly the lightest cars in the world.
My best in my high-mile stock 95 C36, cold water temp, race fuel, no spare, street slicks was a 14.04 at Atco Raceway in NJ in the final round of the Import World Series to take the win against an 11-second turbo Supra (bracket racing). Air was absolutely perfect for drag racing that night and no wind.
I have never been able to repeat that ET and usually find myself in the mid 14s if I can keep traction out of the hole - which is always a challenge.
No Mercedes has the stock ability to be a great drag car, but with an automatic, they make perfect bracket cars. AMGs perform at the top end, no doubt.