I don't have your laptop but I did have problems with Linux which turned out to be nothing to do with the nVidia driver itself.
These lines from your XF86Config-4 file:
HorizSync 31.5 - 57.0
VertRefresh 50.0 - 70.0
If your screen normally refreshes at 70Hz, you may find it is actually slightly higher (mine is nominally 75Hz but is actually 75.2). Having 70.0 as maximum would then prevent it using this frequency. In the case of my monitor 75.2Hz required a Horizontal Sync value of 80.3kHz but my HorizSync line only went up to 79. So it had to use a lower refresh rate and looked horrible!
If you have a Windows dual boot there may be a way of checking the figures (in my case it was by pressing the screen setup button). Or you may be able to find something in your documentation, on the Web or from the manufacturer.
The range of numbers in the two lines above must include your optimum vertical refesh and the corresponding horizontal sync rate.
Your external monitor may have a different sync rate (why it works OK) and when you use the 2D nv driver it may have less to do (why sync less critical).
On the other hand, I am no expert, and just know what worked for me. I could be completely wide of the mark!
Hope this helps.