1k lines does not stress many editors. It only stresses emacs when the major mode is doing lots of stuff to highlight and format.

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.