It is true, yes. Due to the need to have equivalency formulae for Turbo and NA cars, all GT cars are fitted with intake restrictor plates, that limit the airflow into the engine. Because the road cars did not need this restrictor plate, they were more powerful.
However, the race machines were lighter, and with more competition-derived components (e.g. carbon brakes), and therefore the competition machines would be faster in real driving.
The ultimate McLaren F1 is the LM, of which only 5 were made (I think), and all were painted in McLaren orange. Now there's a car you'd swap your Grannie for!
