"IgnoreEDID" is not a valid option anymore. I think you want UseEDID
. Also, the option needs to go in the Screen or Device section, not the Monitor section. However, both your ModeValidation line and "UseEDIDFreqs" "FALSE" should have overriden those checks. What did Xorg.0.log say was the reason it was rejecting the mode when you enabled verbose mode logging?