Not sure about Gb of throughout makes editor memory representations unimportant. Just this week my friend said he kill emacs with a few-MB text file. I was astonished that a software of that esteem would struggle with that.
In my first job I would routinely open 10-20 MB files in Emacs. It handled it just fine. I mean, it gives a warning that this is considered big, but I ignored it.
Now if you open a large text file in something other than text mode, it could bring it to its knees depending on the mode. As an example, opening an XML file in the nXML mode is quite expensive, because nXML mode is powerful and utilizes your XML structure. I just tried a 12 MB XML file and told it to go to the end of the file. It's taking Emacs forever to do it (easily over 30s). But if I switch to text mode for that same file, it handles it just fine.
I just tried an 800 MB text file. It handled it fine.
The one thing where you can easily get in trouble: Long lines. Emacs cannot handle long lines well. Kinda sad.
