Originally Posted by spearfish25

The level in the tank doesn't change very much when the engine comes up to operating temp. So personally I'd rather have it at MAX with a cold engine, than have it at MIN with a hot engine. There is a lot of extra room in the tank above the MAX point, so it won't overflow.

You may have had some air in your radiator that was finally bubbled out with your high-rpm track day. Then when things cooled, the radiator pulled coolant from the surge tank back into the system and the level dropped. Or you're burning/leaking coolant, but you'd have signs (smoke/puddle).