I've recently moved from `vim` to `Emacs` because I want to use `org-mode`. I opened a ~10000 line, 50kb file in `Emacs23` `Org-mode` and proceeded to add about 10 first-level headings. Performance on a quad-core with 3GB RAM in Emacs23 under Ubuntu 10.04/32bit was so slow that it was unusable. I found [two](http://thread.gmane.org/gmane.emacs.orgmode/28097/focus=29447) [threads](http://thread.gmane.org/gmane.emacs.orgmode/37860/focus=37864) on the `Org-mode` email list discussing this. It seems that enabling `linum` causes the slow performance. I can live without line numbers in `.org` files if I have to, but I don't want to disable line numbers for all files I edit. If I'm going to "live" in `Emacs', I'll want line numbers for all other files. 

How can I disable `linum` for some or all `.org` files only? Is it possible to do this if I have several files open in `Emacs` and switch between them? I found some discussion about disabling line numbers for major modes [here](http://www.emacswiki.org/emacs/LineNumbers#toc8), but there was nothing that I could implement (although the `linum-off.el` script [mentioned](http://www.emacswiki.org/emacs/linum-off.el) on the page looks promising, I don't (yet) know (E)Lisp, so I can't change it as I would need).

I updated `Org-mode` from version 6.21b which came with `Emacs23` to version 7.5, but it made no difference. Performance in `Emacs` GUI is so bad that the application fails to respond at all. Performance with `-nw` is "better", but still unusable.