Just completed up to 76% level with the other cars in the series. 

But to finish the last three cup races, starting from PR 44 finishing at PR 50, you need the new Porsche Cayman S to get to 100%. Reward is 22 GC. 

Might be worth it to upgrade it till PR 50 for the Gauntlet, depending on what the GC reward is for the gauntlet.