I have a G35 Coupe but test drove the Sedan as well, both have a lot of get up and go. While you won't have the clutch action like you would in a MT, the automatic does give you quite a bit of versatility. I would highly recommend a G35 or 37. You can definitely find one well under your price range too.
Another option is a Nissan Maxima. We had one about 5 years ago, plenty powerful and very smooth handling.