I'm sure you've seen it, but just to be sure - there's an IntelliJ plugin that gives you vim key bindings: http://plugins.jetbrains.com/plugin/?id=164
Also, I found it really slowed things down (in RubyMine), sometimes updating just 1-2 characters a second in a big project (on a modern MBP).
I've gone back and forth, but generally I prefer Vim with Janus distro, albeit I miss a lot of cool things from IDEA.
I just upgraded from a "modern" macbook pro (2008, aftermarket SSD) to a "modern" retina macbook pro that is maxed out. IntelliJ and RubyMine fly like the wind on this new machine. The old one was painful to use IntelliJ but you could live with RubyMine performance.