I think it's a combination of a larger window, antialiased text, arguably better font, semi transparent background, terminal being 256-color (or more), and so on. By passing -a I get it down to 80% CPU. This is progress, guys!
I have all of this except the transparent background. But that should be a compositor thing, independent of the window contents. That's bizarre, pushing a few thousand characters to the screen shouldn't, by far, reach 80% CPU usage. There's something in your system that's really botched up.
I tested again, it's Terminal.app doing something! I tried with iTerm and CPU usage is negligible. Wonder what it is doing. My system is otherwise very fast.
