Yup! They were indeed the fastest. "Production" applies to marques that had a certain amount produced, so an exotic that they only made 20 or so wouldn't qualify.
The program was killed for 2 reasons:
1. GM had already planned to kill off the rear-wheel drive G-Body platform (Cutlass, Monte Carlo, Regal, Gran Prix)
2. The prima donna Corvette division was whining that they weren't the horsepower/speed champs at GM anymore, and demanded the Buick program be disbanded.
The powertrain made another apearance in 1989, in te Pontiac Turbo Trans Am, (albeit with FWD cylinders heads to get more shock tower clearance), and that car is the only Indy 500 Pace car to require no modifications to keep up.
They deliberately rated the HP figures lower to keep the Corvette pansies quiet, and to stave off increasing insurance rates. The rated figures were taken from the rear wheels, where all other cars are rated on an engine stand, at the flywheel. Figure in approximately 30% drivetrain loss, and you can see the cars had MUCH more than most everything oout at the flywheel.
It's not only the HP, it's the MASSIVE torque these motors put out, somewhere in the 400ft/lbs in near stock form.
It's not true that they "eat up headgaskets". It IS true that once you DO blow the factory head gasket, you have to be more careful. IF the car is tuned correctly, and care is taken, they will take 20+ lbs of boost everyday, and a little more.
MUCHO info -
http://www.gnttype.org
Oh - and "Grand Nationals" aren't mechanically different than standard Turbo Regals, it's just an appearance package.
<---- Has owned and driven TR's (Turbo Regals) for over 10 years.