I can get an undistorted screen display if I let the monitor set the aspect ratio automatically,
Interesting note. You should take a look at file /var/log/Xorg.0.log, searching for the effective resolution choosen from xorg,
mine show a line like:
(II) May 22 10:01:29 NVIDIA(0): Initialized GPU GART.
(II) May 22 10:01:29 NVIDIA(0): Setting mode "1440x900"
(II) Loading extension NV-GLX
if you will find that the resolution is 1366x768, that will means your monitor is getting fooled at some point ...
Also, you should find in the same log file other info, like screen resolution "offered" by your monitor ...
i.e. mine is showing something like:
(II) May 22 10:01:28 NVIDIA(0): Assigned Display Device: DFP-0
(WW) May 22 10:01:28 NVIDIA(0): No valid modes for "1280x800"; removing.
(II) May 22 10:01:28 NVIDIA(0): Validated modes:
(II) May 22 10:01:28 NVIDIA(0): "1440x900"
In my case I will not be able to use a 1280x800 mode ... because not supported by my monitor.
About the differences between Linutopt4 and PCLinuxOS, they are probably using different xorg version... and therefore different results.
I do not see anything wrong in your xorg.conf files.