[Big Dave]

A T-56 is a six speed made by Tremec. It is used on a lot of high performance cars. Essentially, it is a close-ratio four speed with two overdrives on it. Fourth is straight-through. Fifth is 0.72:1 IIRC, and sixth is 0.5:1. It does exactly what you are looking for - gives you great quarter-mile performance AND low-revving economy gearing.

Corvettes do not use the T-56 but they have been in Camaros, Firebirds, GTOs, and Mustangs for years. They will probably be availalbe on the Pontiac G8. You can get rebuilt or remanufactured T-56s if cost is a big item.

With OEM-sized rubber you can expect 1200-1500 RPM @ 60 MPH depending on your axle gearing.

I was always under the impression that a T-5 is a throwaway and any work you put in it will cost more than it is worth.

The other workable alternatives are:

Regear the car to 3.08 or 2.73.
Install a Gear Vendor or US Gear overdrive

If I had a pony car I loved I'd be thinking T-56. I even briefly thought about one for my diesel but it is not heavily enough built to take the sustained loading a diesel can put on it.