Well the thing is, Gnome runs KDE apps by keeping a chunk of KDE running in the background all the time. I think a pure-Gnome system would be faster and more responsive without that extra overhead, but then you'd have to pretty much kiss off any KDE apps you might be attached to. I think anyway. I'm not an expert, but I'm quite sure there's at least a few KDE libraries kickin' around in any hybrid Gnome/KDE setup's background. And vice versa of course.
I'm running the KDE/Gnome version here, and I do use a few KDE apps, so there's gotta be some compatibility stuff running on my Gnome, but overall it still feels a lot lighter and more responsive than KDE, so I guess it's not a HUGE overhead. (Runnin' XFCE too, for that matter...
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