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Put effort in turning kwin into a lightweight window manager like openbox (I've used openbox in kde and it feels very fast).

Actually in my laptop, Compiz runs better and faster with full desktop effects than kwin with minimal effects.

I think kwin is a great wm and KDE would be better if kwin is faster.

Sorry for my poor english.

"improve performance of X" isn't a valid idea because there is no way to determine when it is done, and it is always "in progress" since developers are always trying to tune performance.

There are several window managers faster than kwin, metacity, openbox, xfwm4 and even compiz. So i think its not an X problem.
In KDE 4.6 there was a KWIN performance improvement. That's what i ment.

By "X" I didn't mean "X11", I meant "insert random bit of KDE here". General requests for improving the performance of KDE as a whole or particular bits of KDE are not valid ideas, for the reasons I listed above.

If you can list specific changes that would improve performance, then those might be valid ideas (or bugs, depending on the nature of the change), but general requests for performance improvements are not.