One thing about this particular benchmark is that the file it produces is a little bit unusual even for large text files, because it is only contains one (massive) line. Most huge text files you open in text editors are things like multi-gigabyte logs and database dumps, which are composed of many relatively short lines. Text editors often bake that assumption into their data structures. A more representative test would probably be to use hexdump instead of base64 there.

Though I take the point: if a text editor advertises itself as being "fast", this is the kind of stuff you expect it to handle.

EDIT: ok, so i just tried the hexdump version. Vim and Emacs took a couple of seconds each (Emacs being slightly slower and chunkier when you navigate, Vim handles it without issue and is perfectly repsonsive). less opened it instantly (obviously, it's less!). ox has been going for a few minutes now, nothing happening.

It's not the benchmark's fault, ox is just slow for large files.