Pseudo terminals inherently have some overhead compared to native kernel terminals, but in practice I don’t think it’s much of a concern. That said, I don’t claim to understand the inner workings or where performance difference may lie.
Eshell vs a conventional pseudo terminal, however, is no contest. Go with the conventional terminal when you need performance.
Do you mean the ‘normal’ shell in Emacs (which in SpaceMacs I can get to by SPC ') vs the eshell? (That’s what I was referring to - sorry if I wasn’t clear).
Ah, no I misunderstood. I was talking more generally about Emacs as a terminal vs dedicated pseudo terminals. I assume SpaceMacs’s “normal” shell has performance properties resembling eshell because eshell’s bottleneck is almost certainly Emacs and its concurrency limitations. Can’t say from experience, though, since I haven’t even got SpaceMacs set up yet!
For fun I ran a quick benchmark test in my Ubuntu 16.04 VM. I’ve noticed programs with a lot of output tend to go slower in eshell, so I ran the following command in both eshell in a fresh Emacs instance and gnome-terminal, both with my default login shell (zsh). It repeatedly prints y\n for 5 seconds, displaying the results and writing to a file.
$ timeout 5 yes | tee -a $file
Comparing the number of lines printed to each file:
~ $ wc -l emacs
1148639 emacs
~ $ wc -l gnome-terminal
5963776 gnome-terminal
~ $ (/ 5963776 1148639.0)
5.19203683663884
Gnome-terminal did 5x more work than eshell.
Currently using VS Code, however, I’m challenged to move to SpaceMacs, just dunno with what start 
Used to use Atom, it has nice plugins, but not so stable, as I’d wish. Currently working in VS Code + Dash integration.
For those using Visual Studio Code instead of Sublime Text 3, do you not feel that symbol search is a worthwhile feature? Every time I try VSC out, that stops me cold. Though the lack of an ‘origami’ plugin also hurts. It otherwise looks nice.
I started using VSCode full time a couple of weeks. Before that I was using spacemacs (Hybrid mode) for a good year and a half. I loved it (and miss it), but the performance of emacs was getting to me. VSCode feels just as fast as I remember Sublime Text being before I switched. I just wish there was spacemacs, but for VSCode 
VSCode gets better every release.
I still miss spacemacs though, haha