For interactive use, profiling is as simple as M-x profiler-start, doing what causes the slowdown, and then M-x profiler-report.
In my case there's nothing slow but IO, I should try on another windows laptop with a faster SSD (mine is low grade) to see what is what.
[1] https://github.com/bbatsov/crux/blob/master/crux.el#L496
I can edit multi-thousand line (5k+) Org documents just fine. So it's probably the major mode or some minor mode(s), or a combination.
Anyway, the workaround I have for the occasional time I have huge things to paste is to switch the buffer to fundamental-mode before pasting, and then switching back.
As a curiosity, what kind of things are you pasting that are that big?
I’ve found that the reason why large files are slow is due to formatting and linting and not the size of bytes on disk.
With fundamental mode and no line numbers it feels as fast as Vim or Sublime to me.
I regularly used other editors on C files with 30k+ lines, 15 years ago when machines were slower.
Emacs' real weakness is an over-reliance on regexes for highlighting and poor integration with sources of semantic and symbolic information for richer highlighting, editing and browsing. That, and synchronous operations for the same.
but folks here are talking about _each_ line >1k characters, not total number of lines in a file...
A quicker emacs would be neat, but most of the time emacs gets speed from flexibility (it might be slow but I can automate something) and design decision (magit for instance blows 99% of the fastest git interfaces)
ps: one part that realize is that I don't like emacs daemon, and even curated my setup on windows (probably the culprit) takes a few seconds. It's not slow but often I want a buffer right away so I use notepad u_u; stupid I know.