in ST3 beta, one issue i faced was large files that changed frequently, like a log file. ST3 would neither keep the uncharged version, nor just append changes, but load the entire file from scratch and show me loading bar every time the file changed.

Notepad++ handled that surprisingly well. pretty much the only time i had to use another text editor besides ST

How large are you talking? I had similar issues early on with Atom, but I don't have them anymore (same project). Also, it would only hang for about a second when initially opening the file, later on it would work smoothly.

Big JSON files for one, with tens of thousands of rows. ST3 can load and regex replace nicely. Atom just was unresponsive.

To be fair, I forgot I got a new PC between the first time I used Atom and when I switched over to it.

However, I did try opening an 11 MB (JSON) file and it did indeed feel sluggish.

I'm using ST because I want to use the same editor for my code and data, and I rather frequently get 100mb-1gb textual data files, logs, tabular data in plaintext or json, etc - not big enough to require special tools to process (I mean, they're a small fraction of my RAM), so a text editor should allow to eyeball them and do some basic processing - edit a particular line, do interactive global regexp replacements to e.g. adjust the columns in a million-line file, etc.

I haven't tried Atom, but the Hydrogen plugin looks very interesting. How does it react to, say, being asked to do syntax highlight on a 100mb json?

Many-megabyte, probably; think an assembly dump of your browser, for instance.

Not sure why you're being downvoted. Sure, maybe you're not going to have a need to open an assembly dump of your browser very often, but plenty of projects have multi-megabyte text/data files that need to be opened now and then.

One of programs I develop uses a dictionary that when unzipped is ~8Mb. Sometimes I need to open that up in an editor and it's nice not to have to fire up a different editor to do that.

In fact this is one of the first things I do when trying out a new editor - see how well it can handle files > 1Mb in size.

Maybe if you're only working on small projects with small files this isn't such a concern, but there are plenty of people who have legitimate concerns if an editor can't open large files (and 1Mb isn't even large).