Hi 84R7
Gringo was trying to help you out based on the title of your post which reads 6400 GT.
(maybe you could amend the title to read correctly?)But well done for sorting your problem, and thanks for mentioning the GraphicsEnabler boot option=n conflicts with using a device (EFI) string... though I and most people here probably wouldn't have both options in the com.apple.Boot.plist at the same time (even though you had the string set to No).
But remember RC5 is still pre-release and things are likely to change, so to make the most of the public development and report issues for RC5 I recommend, if you want to of course, is to register and post the issue at the
issues section of the repo.
Regards