I do admit that once mastered, the 787B is very fast, I did all of Mistral 78 lap endurance with it and I got extremely good at using it.
But, the R390 (which I did SS 11 50 lap endurance) was much easier to get a lap time that was very close or as good as the 787B. mainly due to the R390's excellent behaviour under HARD braking and predictable corner exiting.
The GT-One is also extremely nimble and can take those longer sweeping turns in GT3 with WAY more lateral grip than either the R390 and especially the 787B.
However, the 787B has that awesome throttle-off tail-whip turn-in which is why I used it for Mistral with all of those 90 degree turns, but if you took it onto lets say Complex String or a course with high speed sweeping turns, it understeers like a mofo.