I have the Chevy Impala with the 3.8L V6 (non-supercharged). The tranny is ok for a four-speed auto, but you really have to rev it to expose the power. It gets 30mpg on the highway, so I don't complain about that. Why don't you include the Impala SS with the Regal and Grand Prix? They're all W-body cars with the same engines and the same transmissions afaik.
The Impala SS has a 5.7L engine, which if someone is looking for a relatively cheap car, I doubt they'll want to spend a lot on gas.