I'm quite out of touch in terms of mods, not sure if the N.400S GT4 mod exceeds any limits or if relevant at all..., just my two cents:
Yesterday during Round 1 of NDR GT4SC, we had a lot of Shift+P/joins during the semi-hardcore qualifying, and the stutters were not pleasant at all while driving (doing actual hotlaps). I don't have a weak system, and still get those stutters with a lot of mods. Again, I have no idea if this specific car has all objects within limits or uses some exploits, no idea.
If that pretty detailed car adheres to all mesh-relevant limits, then no way I would even think about raising any limits. Optimize your models, people, do the work - proper modding is not just about throwing in a random, hyper-detailed mesh you just found, calling it a day, and when problems come up, starting to blame others for the work you have not done.