Yeah, my own experience is something like that. Kubuntu is one of the worst KDE based distro I have used, though it's not so bad as to render it useless (the usability of the core Ubuntu outweighs most faults in my opinion). Never bothered with Arch, but I agree that OpenSuse has one of the better KDE desktops out there. I would follow that with Debian/Sidux. Fedora is alright and still better than Kubuntu, but it's definitely not among the best.
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Power & Memory Usage Of GNOME, KDE, LXDE & Xfce