I am no expert and do not have that card. I did a search and seems it uses the 96.xx drivershttp://www.nvidia.com/object/linux_disp ... 43.16.html
I may be wrong in my search, just what I came up with, would not hurt to try them and see if they work.
The link I post is for reference only, do not use it to download the driver.
In a root terminal, "equo search nvidia" and equo install the 96.xx drivers for your kernel.
eselect kernel list and then uname -r make sure they match
eselect opengl list and set nvidia ( I know you already did but humor me)
nano /etc/X11/xorg.conf make sure that every instance to drivers says nvidia and not nv
then equo install the 96.xx drivers listed
This should work, let us know how it goes. If you still have issues they can be fixed.