Eclipse takes a while to get started. I find that once it's up and running, performance is good though, I don't notice much UI latency in normal use. I've disabled spellchecking and variable match highlighting because I'm not fond of the visual noise those features add; as a bonus, the editor feels slightly faster too. What can be slow at times is code model parsing, but as it runs in a different thread than the UI, it doesn't bother me, and I can live with syntax highlighting needing a second to update.
Eclipse can be overloaded with plugins though. Particularly those which constantly scan the text you're working on can slow it down noticeably.
The smaller, faster IDEs usually pay for it with lack of useful features. They often lack good refactoring support, or version control integration. There's always a trade-off. I suppose it depends on the size of your project what's most efficient for you in the long run.