Just a little opinion
If BJ keeps fighting and stays at lightweight no one can beat him. Florian is a great LW but BJ will destroy him.
The problem in the GSP fight was GSP. He is a so massive and fast and talented. He is a bigger, better BJ Penn.
BJ is faster and stronger at LW because he is forced to be in shape that is why 155 was perfect for BJ he needs to go back there and secure his legacy again. His record isn't steller and it doesn't reflect how good he really can be if he tried.
Going out now is a bad way to do it and fighting GSP again for the same if not worse result won't do him or his legacy any good.