Do a search, and there's tons of info. SRT6 vs stock six speed .........there is no comparison, and until recently it was not easy or cheap to change to forced induction on a NA. Since then there is a company offering a turbo for the NA, however the SRT6 is more than just an engine change as the entire suspension and drivetrain is uprated.
Drive the autostick and it may convince you that a manual is not absolutely necessary. You can also add a paddle shift kit if you feel the need