I've started playing GT4 again as my interest in GT7 starts to fall away.
New save got me a few cars and I used the NISMO 270R in the Sunday Cup, easy, and the FR cup, not easy, I lost two races. Seattle reverse I got 3rd and Laguna Seca where I was 2nd. After I'd won the other races I went back to the Seattle race, got a different field, and was able to win. Laguna Seca took two more attempts to win.
After that I tried the first race in the FF cup. Finished 5th. I gave B-spec a go and it finished 6th. I redid that race myself and got a win. After a couple of robust overtakes. This is a much harder game than GT7.