Even though I'm mostly a Gnome user, my LaTeX editor of choice is Kile. Unfortunately, it can become a bit sluggish, especially when dealing with long lines. (I hate artificial line breaks, so I just type one line per paragraph and turn on dynamic word wrapping.)
This seems to have something to do with rendering. To make Kile considerably faster, start it like this:
kile --graphicssystem raster
Instead of raster, you can also try opengl, which is supposed to be even faster, but not considered stable yet. YMMV.
