Ouch - your xorg.conf is crap
I've seen this before and it's the result of some fallback mechanism if everything goes absolutely wrong
I assumed you had a reasonably correct xorg.conf
However my advice is the correct solution to get better refresh rate
Somewhere in the forum there is a solution to this, but I can't expect you to find it, not to hard thoughviewtopic.php?f=18&t=6958&hilit=Failsafe+Monitor
And as it tells you in that topic and in your topic
# You should use dexconf or another such tool for creating a "real" xorg.conf
# For example:
# sudo dpkg-reconfigure -phigh xserver-xorg
And sudo dpkg-reconfigure -phigh xserver-xorg gives you decent settings back.
Now you have to install the nvidia driver again, but first back up your now working xorg.conf
First when everything works add the Twinview false line
If you can't log in to a normal x session you can start in "Recovery mode" - and now you are root - take care so you don't mess up.
You can run dpkg-reconfigure -phigh xserver-xorg in "Recovery mode" (no sudo - you are root already)
When you are done reboot - nothing else