I use Sublime Text 3 for coding on LibreOffice. With over 225000 files and 23000 sub-folders you could call it a big project For testing the performance of both editors I opened up the main folder in Sublime Text 3 and Atom. All source files are cashed and I opened 20 tabs with huge C++ source files. This is the output of top:
VIRT 447396 RES 171672 SHR 5456 CPU 99,8 Memory 1,1 sublime_text
VIRT 441452 RES 165960 SHR 5456 CPU 99,5 Memory 1,0 sublime_text
VIRT 2397364 RES 278060 SHR 101064 CPU 4,0 Memory 1,7 atom
Sublime seems to use a lot more ressources to deliver its fast performance. Atom is a lot cheaper in CPU power but uses a lot more memory (especially with a low number of tabs).
A search through the whole code base with atom takes ages (even with ctag plugin) and Sublime is a lot faster (not lightning fast, but definitely finishes the job faster). In addition the search results on Sublime are much more refined and polished. I need to search the code base on a regular basis and need my results fast and organized. A job in which Atom really sucks. Especially because Atom shows you all results in the .tags file as well -.- That causes the search results "file" to be larger than 2 MB and Atom kicks out... For me that's the killing blow against Atom.
For small projects Atom might be okay. But if you start to use an editor for huge projects you definitely should opt for Sublime.