After I had wrote my reply, i saw the other Thread in the Linux-area. There I found the solution.
I've installed only the packages nvidia-glx-legacy, nvidia-kernel-common, linux-restricted-modules (your kernel version). Then I made sudo nvidia-glx-config but it said, i had the wrong kernel. So I installed the build-essential package and it worked and said i have to change the Driver from nv to nvidia in the xorg.conf. After that i had exactly the same problme like you. Then I put the Section Extension in the xorg.conf like you describe it and now it works.
I haven't installed nvidia-settings, nvidia-xconfig.
You said your 3D-graphic is slow and uses to much CPU. glxgears -printfps shows me 620FPS and the CPU-usage is 100%. With dapper I had 650FPS and also 100% CPU-usage. So there isn't a great difference.