Back when I first tried this race I used the overkill 930hp GTO TT, that car was invincible for all other races, except this one. I learned the hard way not to rely on power alone. Sure this car is fast when the tires are green, but once it turns yellow its handling suffers drastically and from yellow to go to red it just takes a few laps (because you continually understeers and plows into the gravel, which speeds up the tire wear). But I managed to hang on until the 57th lap, my tires are totally red at that point, and the AI GTO TT with ~600hp passed me on the main straight. I pitted the next lap because the car was undriveable, but it was too late. I placed 2nd. 2 hours work gone just like that.
Then I reentered the race with the GTO LM, and I won.
Like I said, balance is what you want. The GTO is fast, but it's (wayyyy) too heavy and all that weight is hard on the tires.
Conclusion: pick light cars for endurances so your tires last longer, also, avoid 4WD/FF cars as they understeer like mad when the tires are worn. FRs are the best because they turn easier when the tires are worn (watch out for fishtailing though).
Smooth driving style helps too.