The usual extra info...
There are 54 events (52 Trophy + 2 TT) and the rewards 25-50-75-100% are split 8-13-18-27GC.  You will need both cars for 100% but a fully upgraded Testarossa alone gets you to 75% and beyond:

PR49.6 will be needed to win the Bugatti in its LTS when it happens...that will be enough for the cup races on tiers 17-19, but of course not the final one at PR53.1 in tier 20.