I thank everyone for their advice and answers. In the end I flew to FL310 but I have to confess that I did something cheating, the day I could do the flight of that duration, had very bad conditions of wind against and crossed up to 60 knots, I was not going to be able to reach my destination, I modified the wind in Xplane to have a tail wind of 30 knots and in the end I arrived without problem. For the rest of the flights, I exclusively use Xenviro.
Thanks for the link, it seems very useful.