Earlier quoted context omitted.
It seems to be mostly an Atom problem. Brackets and Lighttable built on same technology are way faster.
Brackets also feels slow compared to ST. Switching tabs has a visible delay (up to 1s) for me.
Everyone says it is DOM rendering that makes these editors slow. Since Reactjs just announced native support for android and ios, I'm wondering if this can be applied to the desktop for much better desktop app performance.