There's actually no such thing as a GTO Judge 427 because the 427 is a Chevy motor. GTO Judge's came with 400 Pontiac big blocks from 1969-1970 and 455 Pontiac big blocks in 1971.
The top speed mostly depends on the car's rear gear ratio. Muscle cars are not known for their top speeds because they only have 3 speed automatics or 4 speed manuals without overdrive. A GTO Judge with a 4.11 gear ratio might only reach a top speed of 120mph, but be extremely quick in the straight line. While a GTO Judge with a 3.23 gear ratio might reach a top speed of 140mph, but have slower acceleration.
If you want a GTO, I wouldn't buy a rare original Judge car because you'll end up spending loads of money for a car you'll be cleaning with a tooth brush and afraid to drive in the fall because the leaves might scratch the finish. If you like the "Judge look", I'd buy a regular 1968-1972 GTO with a 400 or 455 engine. Believe me, you'll save lots of money and won't be afraid to enjoy it!!
Hope that helps!
