My reference large text file is 182,516,761 (174MB) bytes long in over 5 million lines. Editing it will crash almost any app you commonly use. Usually it will also bring the entire computer to a halt.
For example, none of Microsoft's text editors, like Notepad, Wordpad, Visual Studio, and especially Microsoft Word, can handle a large text file. They will all hang and lose data. On Windows I use a shareware app called TextPad that I bought 20 years ago and it does a very decent job on large files. I am using an old version (4.7.3 from 2004) still and it works great. Considering how much I use it, this was an excellent $15 investment in shareware, although I see it has gone up to $27 now.
Apple's text editors are just as bad. Xcode is horrible, and TextEdit can hang as well. Xcode will just start paging gigabytes of crap to the disk and the whole machine becomes just as unresponsive as Windows can become.
So what to do? Well the vi editor known as vim on FreeBSD, Mac OS X, Linux, and Cygwin on Windows handles large files with ease. Vim is available in a GUI version, but I love a command line world so I only have experience with vim in a console or terminal. The GUI version may not perform as well, I'm just not sure.
The best text editor for large files? The MPW Shell was the best of all text editors I've ever used for opening large text files fast. The MPW Shell was so good because it never tried to keep the whole file in memory, and it would only page in the parts that were needed. Of course one of Steve Job's worst decisions (along with cancelling HyperCard) was to kill the Macintosh Programmer's Workshop, or MPW. Steve's software decisions were not infallible! Alas MPW died with Mac OS 9, so it is no longer an option.
I have found a very nice text editor that is free for the Mac called Eddie. Version 3.1 just came out. You can get it here. It actually has a worksheet file like MPW had, and it runs bash in it. You can actually do something like MPW's "selection expressions" and pull selected text from a window and redirect it to a command in the worksheet. I spend a lot of time in Eddie. Eddie 3.1 can open my reference text file in 18 seconds cold, and after that it only takes 3 seconds on a 2.9 GHz Core i7 iMac. This is the fastest time of any GUI text editor that I have seen. (vim will do it in about 2 seconds on the same Mac.)
There is one system on the horizon that I want to play with more. It is called Xiki. A three minute demo video about Xiki is available here. It reminds me a lot of MPW, which truly was the best development system ever. It is interesting because it puts an interactive twist to the command line.
Created: 7 Aug 2015, using Eddie on my iMac running Yosemite. Modified: 9 Jan 2016, using Eddie on my iMac running El Capitan.