That's one hell of a braking zone. I can't think of another track that would be that brutal on brakes. Ignore that, missed the supercharger part in the description.
The pedal going to the floor suggests that the brake fluid boiled, fluid doesn't compress, but the "air" after it boils does resulting in a very long pedal.
Did it remain long /spongy afterwards, if so that's probably the cause.
If not, you probably overheated the pad material which would have resulted in it having a huge drop in friction so pushing the pedal would result in far less braking force.
New pads will have a large impact, the stock ones just aren't up to heavy track abuse, particularly in a super/turbo car. I think of those that track the car and have gone the FI route they all have a BBK. The dot 5.1 would help prevent the fluid boiling, depends which of the symptoms you had.
Unrelated, but if you don't have an oil cooler you may want to keep an eye on oil pressure /temp when on track if you don't already.