As a workaround you can change window behaviour to not show contents during moving/resizing. In KDE this is in System-settings>Window Behaviour>Moving.
But yes, you have enough hardware for this not to be an issue. I suppose we’ll have to wait until a fix is found. 
I have a problem with high usage of CPU as well.
After updating to 11.4 my average usage of CPUs (I have 4 of them) is around 50% in idle mode! In the past it was 2-3% max.
What’s going on?
Here is the proof.
http://pricesincyprus.info/rozne/myCPU.png
@GazetaCypr: check out what process is hogging the CPU. You can do that with top in the command line or with CTRL+ESC in the desktop.
It’s usually X, kded, prepare-preload or something flash-related.
Does it improve if you disable 3D (ALT+CTRL+F12)?
I have the same issue with firefox.
I am unable to work with kdenlive either. If I import a video and wants to play it, both processes (kdenlive and Xorg) reach 50 % CPU usage and the video playback starts to lagg.
Is it possible that this is realated to a wrong xorg settings?
OS: Linux 2.6.37.6-0.5-desktop x86_64
System: openSUSE 11.4 (x86_64)
KDE: 4.6.00 (4.6.0) “release 6”
AMD Athlon™ 64 Processor 3500+
2 204,94 MHz
Manufacturer: nVidia Corporation
Model: GeForce 9600 GT
2D driver: nvidia
3D driver: NVIDIA 270.41.06
ps.: I use SUSE since 10.3 and I must say I kind of allways had this “issue” its good to know this is not normal.
I have a same issue with scrolling and high CPU usage. When I scroll in konqueror or firefox my CPU will go up to 50-65% from around 1-3% idol. I have am HP DV6-1280us.