Variant Performance List
AMG GT Coupe - 456hp & 443lb-ft
AMG GT Roadster - 469hp & 464lb-ft
AMG GT S Coupe - 503hp & 479lb-ft
AMG GT C Roadster - 549hp & 502lb-ft
AMG GT R - 577hp & 516lb-ft
So far, from what I've gathered, this is what the breakdown is in terms of simplified horsepower and torque figures.
The variants do have different features as well, such as different suspension packages, different track widths, electronics, etc. But again, this is just a general breakdown.