It's definitely easier to buy just one for CR 500.000 instead of getting all Gold Trophies in Jeff Gordon NASCAR School. Especially when you can make CR 504.000 in about 4 minutes - load times not included
(Ferrari Seasonal Event, Circuit de la Sarthe)
The nascar challenge will get you one and it's a headache but not nearly as difficult as the vettel thing.
I used steering assist for the harder ones to make drafting easier. Worked for me. With the pit stop one you just sort of have to force your way into a spot mid-field that leaves you close to other cars. If there's too much distance you'll never catch up to draft. Good luck!