PHPDesigner 7 is really fast. It has everything you are looking for, except IT'S NOT FREE, but it's really worth the money.
I use it on old machines, where others are really unusable. It opens files very quickly and runs smoothly.
It also has source code navigator (shows you an index of the PHP functions, classes, methods and variables you have defined in your current file), and lets you jump from a function call to the definition with Ctrl+click, just like NetBeans and the big ones. It only lacks code collapsing.
Other that I used in the past: Dev-PHP. Written in Delphi, but very fast also. I found some bugs so I left it, but other users in my company didn't had those bugs, so it was probably my installation only... try it yourself.