It wasn't so much debugging as it was laying our your video card and monitor manual, listing the config file and making sure all the little numbers match up.
The coolest thing one could do with a legacy XF86 config and a CRT monitor was invent new "overclocked" video modes. I had one monitor that was rated for 1280x1024 running at 1600x600 to match another monitor for a Xinerama setup.
