There are two championships:
1) The first is the "Porsche championship", which you can only compete in/ win if you use the Porsche for all seven rounds.
2) The second, separate championship is the "Porsche and Aston Martin championship", which you can compete in/ win if:
a) You use the Porsche all 7 rounds, or
b) You use the Aston Martin for rounds 4 to 7.
There is no separate Aston only class or championship.
Thus:
- If you use only the Porsche, you can win both the championships.
- If you use the Porsche and the Aston Martin, you can win only the "Porsche and Aston Martin Championship".
So for the man who wants to win everything, the recommended route would be to stay in the Porsche.*
* Nothing in this post constitutes racing team management advice or gives rise to a racing team manager/ driver relationship; it is provided for general information purposes only. No driver should act or refrain from acting on the basis of information in this post without first seeking advice from their racing team manager with respect to any particular championship matter.