In 2015, the numbers of 800 scores were roughly 27,500 on Math 2, 7,100 on Physics, and 6,600 on Chem. So I’d venture a guess of 2-3 thousand who scored 800 on all 3, which means such an accomplishment isn’t so rare at top schools like HYPSM (probably on par with the rarity of a 2350+ SAT score).