Uninstall Msysgit and install Cygwin + Git. Then global '.gitconfig' will be here: C:\cygwin(64)\home\[userName]\.gitconfig .
Now you don't have to worry about an environment variable which may be used by other programs. For example, my environment variable pointed me to a mapped drive in my work windows domain environment. I dont want my global .gitconfig sitting on my "home" mapped drive. I also don't know what might happen to other applications that might rely on that windows environment variable. Operations division might need that environment variable set to the mapped drive for a reason.
Also you don't have to worry about Mysysgit overwriting your 'profile' configuration settings if you specify a specific path to global '.gitconfig', using this method.
In general, save yourself and use cygwin bash shell in windows and be happier