Surprisingly, VS Code handles large files quite well.
Just tested it on my Mac opening an uncompressed ember.js (~1.5MB). The file loads instantly and syntax highlighting is done in less than 1 sec. Movement and editing are very responsive.
On the other hand, when I open ember.js on Atom, it takes more than 10 sec to load and syntax highlight, and moving & editing take .2 ~ .3 sec to complete.