It is very slow indeed. And I have the feeling it continues consuming resources even when the page is finally loaded and stabilised, because my browser gets somewhat slower when I have reddit+RES in a tab, even though I haven't switched to that tab in a while.
Have you ever compared the page load times of reddit with and without RES? It's horrific. And adjusting the settings? they have search functionality for the settings because there's so many settings.
The only things I use from RES are the account manager and the subreddit manager. I hate the never ending reddit with a burning passion, and don't even get me started on the highlighting posts that you've clicked on crap.
RES is a bloated monstrosity.