Seems the 50/50 rule applies to your standard auto, but when you get lighter things start to change. For instance, according to this article regarding an FI racecar ...
It was found that a front to rear weight distribution ratio of 40:60 resulted in the fastest lap time.
SpringerLink - International Journal of Automotive Technology, Volume 9, Number 3
... and just when you thought you had it all figured out lol.