Success! Finally now I got everything to work perfectly well.
The problem was, that there must have been something wrong with my driver installation. While glxgears was running pretty fast, the nvidia logo was not showing up whenever xorg would start up. So I suspect something in the internals was wrong. I installed the latest 8173 driver with the standard installer, but then problems "unable to open device /dev/nvidia0" even though the file was there. Repeatedly re-installed the older driver via the Yast Online Update. Then I fixed my xorg.conf file (copy that runs bug-free for days now is attached). Didn't do anything else. Also used Yast2-->System-->Display from inside x to adjust the screen size there.) But now I have 3d accelleration working perfectly well, 1280x800 display and no display issues any more even under heavy use, perfect stability and is keeps working this way. Thanks all who thought about the problem. Maybe the zipped xorg.conf file can be of use to someone. I'm so happy