More powerful than the 450 AMG Sport with 270 kW (367 hp)? 
While willing to concede some details, Moers wouldn't give too much away about how this car would fit into the range. But he seemed to be suggesting a two-tier V6 approach, with an equivalent to the AMG Sport 450 as well as a new higher tune of the same 3.0-litre V6 mass-produced engine, which would add a new niche into the AMG line-up.
http://www.motoring.com.au/news/2015/prestige-and-luxury/mercedes-benz/mercedes-amg-slc-to-go-v6-100077

While willing to concede some details, Moers wouldn't give too much away about how this car would fit into the range. But he seemed to be suggesting a two-tier V6 approach, with an equivalent to the AMG Sport 450 as well as a new higher tune of the same 3.0-litre V6 mass-produced engine, which would add a new niche into the AMG line-up.
http://www.motoring.com.au/news/2015/prestige-and-luxury/mercedes-benz/mercedes-amg-slc-to-go-v6-100077