To onboard VGA change VGA share memory size to 0 MB.
is better or not before installing NVIDIA driver ( at first install )
If you don't remember , launch LIVE CD again and see the different. Live cd /first install using Nouveau (open source )driver.
If better you can try uninstall /deactivated NVIDIA driver from "additional driver"
You need restart after deactivate NVIDIA driver.
check your driver after that with inxi -Gx . It something like :
drivers nouveau unloaded: fbdev,vesa,nvidia
GLX Renderer Gallium 3D at NV44A Direct Rendering Yes
In my experience ( not much
) : nouveau has better compatibility , NVIDIA has better performance