And your modesty knows no bounds!

Tellin' the truth ain't braggin!
I've said it before in RL: had I not had a good night's sleep, I'd have scored much lower. A few different problems, and I'd have scored lower. Just because of higher stress levels. Instead, I was well-rested, and they gave me problems I was able to answer with little difficulty.
(And I went to a high school where I wasn't even in my class' top 50% GPA...but was one of the higher SAT scores in which 75% of us were National Merit finalists.)
Lack of sleep cost me a perfect score on my LSATS: they mail you the results with the correct answers and what yours were- the 3 multiple choice answers I missed, I had the correct answers marked as my second choices in the test booklet. OTOH, I stressed out taking the Texas Bar exam, and had to retake it...more than once.*
I was trying to get into a certain graduate program. To do so, I had to take a particular test. They
called me to notify me of my admission- they had never seen scores that high.
But in the end, standardized tests like that are just a snapshot, and I don't put much credence in their overall accuracy. (They did, however, ensure I haven't had to pay 1/10th of the cost of my education.)
* none of my stress outs were as bad as some of the ones I witnessed, though. One guy passed out at a table near me, and another started laughing hysterically and turned in his test after 5 minutes. Which still doesn't compare to some of the stories out of California...