i've seen problems on a laptop running xfree without framebuffer. When used under KDE, StarOffice 6.0 beta used to crash every now and then, but especially in the presentation module. The problem didnt appear in Gnome though. As for the speed, KDE seems to run pretty well on my computer, except for netscape that sometimes asks for huge amounts of memory (reminds me of the ancient windoze days )

hope this helped a bit