I've found that when pasting in huge files, disabling syntax highlighting makes a big difference. In fact, if you simply open a sufficiently large (I haven't bothered bisecting the size, but a few megs works) xml file, Atom will disable syntax highlighting by default and the performance will be slow but still usable. If you paste in the contents of a large xml file, syntax highlighting is not disabled and the editor either hangs or crashes, in my experience.

Atom should automatically disable syntax highlighting for large files.

Reminds me of old emacs' tricks.

For the gaudiest possible look, then, include the line

(setq font-lock-maximum-decoration t)

Same here, I only get issues after around 100MB.

Most editors start to struggle at such file sizes, which is a shame, but try loading 100mb into Excel. The only editor I found to work nearly instantly is vi; nano takes almost a minute to load large files.

Latest Macbook here, opening files up to 10MB is fine but saving after making any change, even a minor one will cause Atom to hang for a few minutes. In contrast, Sublime has no issues. To be fair to Atom, it has no issues with actual code files in any language; it only struggles with log files and csv dumps. This limitation means I use Atom for most things and Sublime for the heavy files.

Even vi is going to bog down on a file that size if you leave syntax highlighting turned on.