split second loading, saving, editing and searching of large text files
Depends on the use. I'm increasingly using binary formats for things like CPU streamtraces, which can grow very quickly into the hundreds of MBs, and not using a text editor for exploring them. Source files tend to be a few KB, tens of KB if they're in dire need of refactoring, hundreds of KB if they're machine generated (and therefore rarely - but occasionally - hand-edited). As such, I don't mind my text editor having a size limitation too much. It does mean that I can't use it for everything, but most of what I edit is source code of one form or another (including LaTeX).
can log into any host via SSH and just use it
I do this a lot, but I really dislike the fact that I do it. SSH for text editing is an ugly hack to work around the fact that we still can't do file sharing well. I'd much prefer to use sshfs for the editing and only use SSH when I want to build / run code remotely. If Atom came with a nice file browser for remote files, I can imagine changing my workflow.
syntax highlighting and smart indenting
Definitely important. Vim can only do somewhat-smart indenting. Its APIs don't allow you to distinguish between indenting for semantic blocks and indenting for alignment. I like to format my code so that the reader can adjust the tab size without breaking the formatting, so, for example:
if (someLongCondition() &&
(Slashcode's 'code' tag seems to eat spaces and tabs and expand nbsp, so I've no idea how to actually do the indenting) Both lines would start with one tab (or more, depending on the current indent level), the second line would then have 4 spaces. The s and the a line up whatever tab width you want to view the code with. I generally prefer 4, lots of people prefer 8, and some prefer 2 and so this allows people to set whatever they want.