I wouldn't say it's terribly optimistic. Pretty close.
Here's the one that has always correlated best to my own vehicles' dyno pulls and mph at the track, from the CherryBomb website:
http://turbo400.com/cherry/HP_Calculator/body_hp_calculator.html
"Approximate Horsepower Results
Your car weighs 4200 pounds and can complete the 1/4 mile at 141.2 MPH. That means that you've got about 959.2 HP at the flywheel, and about 786.6 HP at the wheels."
It assumes only an 18% drivetrain loss; yours would be slightly higher, so you're in the high 900's with that 75 shot.
Here's the one that has always correlated best to my own vehicles' dyno pulls and mph at the track, from the CherryBomb website:
http://turbo400.com/cherry/HP_Calculator/body_hp_calculator.html
"Approximate Horsepower Results
Your car weighs 4200 pounds and can complete the 1/4 mile at 141.2 MPH. That means that you've got about 959.2 HP at the flywheel, and about 786.6 HP at the wheels."
It assumes only an 18% drivetrain loss; yours would be slightly higher, so you're in the high 900's with that 75 shot.