I already created an issue regarding this on Github: https://github.com/atom/atom/issues/10188
But to give you a quick sum up: I tested VS Code and a clean install of Atom (no extra packages), I was using the Find command on a large file, looking for words that appear often in it.
Atom - search takes between 1s and 1.5s
VS Code - is almost instant, and can also live-update the search results as I am typing
Since both projects are based on Electron - I think it is worth looking into their implementation of the editor: https://github.com/Microsoft/vscode/tree/master/src/vs/editor
I am also wondering whether the Atom team will be willing to make any major changes to the current implementation if that could get us the same performance as VS Code?