The Grass has Always been Greener
Today I read a news post about the KDE 3.5 fork Trinity and it was discussed that you should use it because of the bad performance of KWin:
the one constant is abysmal Kwin performance.
So to me it sounds like the author of said news article things it is a better idea to run the KDE 3.5 fork, because there KWin is without (OpenGL) compositing, instead of just turning off compositing in KDE 4. Well that’s interesting reasoning. (Btw. if you do not run at least 4.7.2 you should not complain about KWin performance).