None of those is a muscle car. Which of the many SRTs do you refer to? The CTS-V is a great sedan with a strong engine and decent handling but not a "muscle car". And do you mean the upcoming 2007 Shelby Cobra or do you mean the current Mustang GT? Neither fits the definition. Incidently a "muscle car" must also be affordable to the masses and most of these are not. Probably one of the most misused words in the automotive lexicon today.

Reminds me of a stupid ad I heard on the radio not too long ago.
An RX-8 was being given away as a prize in some contest, and the clueless announcer kept using such ridiculous lines as "you could drive away in this true supercar", and "imagine yourself behind the wheel of Mazda's new muscle car."