KDE 4.3.4 was released today, one of the more notable changes:
"A bugfix in Plasma's pixmap cache makes the workspace more responsive"
Also, QT 4.6 has been released, and I believe KDE 4.4 is expected to use it:
"Key performance improvements come in the form of a highly optimized, re-written Qt GraphicsView rendering algorithm, a new OpenGL paint engine, WebKit, 2D vector graphic support using OpenVG, and new DirectFB support."
KDE 4 seems to be performing quite well with the 195.22 drivers already, so it should be interesting to see how things improve in the near future.