I think the CTS-V can be called a muscle car, in the same way a GTX or Olds 442 from the late 1960s could.
I don't know what term to use as a generic term for small displacement high performance cars other than "ricer". Rice Rockets are Japanese super/hyper bikes, so ricer, unless you can think of another word. In general, what I call a ricer is any of the cars that the "Fast and Furious" (really, the fast and idiotic) crowd would drive.
There are grandma versions of both the Camaro and Mustang; the V6s (and maybe the Eco-boost 4 cylinder turbo Mustang). Even then, the V6 cars are putting out 300 and up HP; maybe not the 400+ HP of the SS and GT, but pretty fast/powerful none the less.