This is why you use an external editor. You don't get lag, your preview may look closer to the real thing (with custom CSS like the one I made), you get keyboard shortcuts like ctrl/cmd-B for bold, and you also don't lose your post if your tab crashes, or Steemit goes down in the middle of hitting post.
On OSX, I recommend Macdown, and for Windows, Markdownpad
This is very useful, thank you! In a way it beats the word editors, great stuff! :)