So because RubyMine does more than editing, it gets excluded? That seems a bit short-sighted to me. I happen to use IntelliJ for most of my "editing/development" when I need to work on anything outside of the .NET framework.
I may not touch most of what that application offers, but it serves my editing twitch very well and gives me the option of utilizing the other tasks it is able to handle should the project require it.
Everything I see necessary for what most deem "to be a good ruby programmer" is: An editor, a way to write tests, a way to execute tests, and version control. Anything that implements those items and maybe more, seems like a fair contender to me...
I actually almost bought RubyMine, but I already had a phpStorm license and I wanted to get into Python a bit too, so upgrading to IntelliJ was by far the best decision I've made. I'd highly recommend it as an editor (or the cheaper RubyMine product if you don't need to support multiple languages).
So I'm not sure on the distinction you are trying to make between IDE and Editor, to me there is a great overlap between the two.
I've also been spending a lot of time in Cloud9 (again, this may fall under your IDE side, but it is free to use and its editor has been really nice to work with -- gives me quick ways to run/write tests, etc.)