I am normally not a KDE user, but I just gave it a try to see if there is substance in your claims. So I started KDE on a second xserver (running i3wm with two instances of Firefox, one just playing a Flash video, Claws-Mail and several instaces of Roxterm (with newsbeuter and vifm in two of them) on the first one) and opened a instace of Dolphin. It started in about 2 seconds and works blazingly fast, even when accessing the Samba shares of my fileserver.
So I can assure you that there is nothing wrong with KDE on Slackware and that you may be misconfigured either the OS or may be your machine in general.

Default installation from DVD with KDE 4.55 and newer. What i have? AMD X4 955, GTX260, 4GB DDR2. If i had camera i would record it and show it.

Default install of Slackware -current (with some programs added, like Claws-Mail, newsbeuter, vifm, nothing that makes the computer faster), nothing configured in KDE but changing the theme for making the KDE apps fit better with my GTK theme. Phenom II X6 1055T, HD6870 (radeon driver, no fglrx), 16GB.
KDE should not be much slower on your machine than on mine. But from what I have heard the newer versions of KDE should be faster. May be you tried a newer KDE version on Kubuntu?

From my personal experience (I used Ubuntu, Debian, Arch, distro-hopped some time and now use Slackware) I can say that Debian is faster than Ubuntu and that Debian and Slackware are more or less on par in performance (not some crap measurement like boot time).
I don't have proper benchmarks for this, just my experience.

This has been exactly my experience as well. Debian and Slackware have always run faster than Ubuntu.
For some reason, the Ubuntu developers have been obsessed with making Ubuntu boot faster and shut down faster; but they do not seem to be doing anything to improve the performance of the system once it is up and running.
For me, having a light and responsive system is more important than shaving a second or two off the boot up time.

Hold the presses!
It has recently been reported that Ubuntu 12.10 will include some performance improvements:
http://www.phoronix.com/scan.php?pag...1210_ups&num=1
I will be eager to see how this plays out.
Note that it was reported as early as the fall of 2008 that Ubuntu was getting slower:
http://www.phoronix.com/scan.php?pag...nch_2008&num=1
Newer versions of Ubuntu after 8.10 are even slower and more bloated in my experience.

*general bitching, and links just to make the point*.

IMO over the last few years ubuntu has lost a LOT of good users. The sort of users who used to write nice 'how to' guides that were tested and complete. Look at these links for 'how to manually install nVidia drivers with ubuntu'-

http://blog.accelereyes.com/blog/201...-ubuntu-11-10/

That one uses one method to block the nouveau drivers, has get out of desktop, shut down the DM steps.

http://www.overclock.net/a/install-n...tu-11-04-11-10

That one uses a different command to block nouveau, and has a get linux-headers step. No getting out of the desktop, or shutting down the DM.

What_a_mess.

I honestly dont know _exactly_ what you ned to do to manually install the nVidia drivers with 11.10. I dont really want to d/l and install 11.10 just to test what does and does not work......

These days, its got to the point where if you dont want to do things the way that canonical thinks you should do things its not easy to figure out what to do with ubuntu.

They say that, what, every 2nd release?

Since that was written by Michael Larabel (who AFAIK isnt part of the ubuntu cheer squad, though I could be wrong on that), and its citing 'upstream work' for at least some of the (possible) inprovements, maybe its accurate.

We'll see.

Might be. I've been using KDE 4.X with debian sid/aptosid for a long time, and performance does bounce around a lot.....but not by much. KDE 4.8 does seem a touch faster than KDE 4.7, but its not much of a difference.

How much of KDE 4.8 'feeling' a little faster than KDE 4.7 on my system could be due to nVidia closed driver improvements, I really dont know. I do know for a while the nVidia drivers did cause performance regressions.