Not quite, it varies from distro to distro.
When I was running redhat 9 it was XF86Config, but now in mandrake 9.2 it is XF96Config-4
To eliminate any variables, I propagate changes to all of my XF86Config files be they "XF86Config-4" or just normal "XF86Config".
You want to eliminate variables and reduce the known variables as much as possible, try this:
Change the Nvidia driver from "nvidia" to "nv" in your XF86Config file, if GL support dies then you know it is the correct file to use, if GL support is still running, check the other file, conversely if your gl setup is sour then try moving the XF86Config-4 files to another directory, if X starts normally then it was NOT a neccessarly file if not then it is your file to use.
Scientific method is better than ambigous tips, based on general knowledge.
Hope this helps.