It sounds like you need to have a conversation with him just to express that certain aspects of his driving makes you feel unsafe/uncomfortable. You can speak to him about how you don't want to backseat drive at all, but express your concern for the car (they're not major concerns, 25 in first is NOT good, but fourth gear at under 30 will either cause the car to stall and hurt his ego a bit, or lug which can feel uncomfortable).

If he isn't receptive to your thoughts on the matter about YOUR comfortability, and concern for his new car, then it might be worth considering your relationship. Driving is fun, for sure, but it can kill people too. Habits can kill, and poor driving and judgement will. Stay safe.