Here are some tips for the Ferarri 599 Novitec Rosso. I was really struggling with this game but have now accumulated $1.8m via the "online" mode using this method, it allows you to win virtually any race on the 1/2m mode.
The car is maxed on all upgrades, but since the online mode pits equivalent level vehicles at you, this technique will probably work regardless of upgrades.
* Try to get a perfect launch.
* Shift up to second instantly.
* Shift to third at 4k rpm.
* Shift to fourth at 7k rpm.
* Shift to 5th at 9k rpm, try to achieve 'perfect shift'.
* Instantly apply NOS in 5th.
* Shift to 6th at 9k rpm, try to achieve 'perfect shift'
Occasionally some opponent cars still win, they seem to whiz past me at the final second, but this only happens probably 3 in 10 races using this technique. I am able to achieve a 1/2m of 12.611s.