Em,
If you are going for max performance you will need to find what your setup will be and what riding style.
I use two different setups
1 for Rally
1 for offroad racing.
Rally I don't like backshift may brakes and hand brake do a better job. I run 24g and A1 I can hit 125kph with co driver
Offroad I want power now, I run 25g and B2. This will spin 27 ripsaws or 28 zillas with no problem.
I have a few mods to up the hp to handle this settings and I like them,
But each person will have a different like, feel and riding style.