Using a completed save file allows you to skip the grind and jump straight into the action with all content unlocked:
All races, hitman contracts, and debt collections are cleared.
Copy your existing save files to a different folder just in case.
While searching for a "100% Save" for on platforms like Chomikuj, it is important to ensure you are getting the right files to unlock everything the game has to offer. This high-octane title, set in both 1978 and 2006, features a massive list of unlockables that can take dozens of hours to earn manually.