Re: Reduced Blanking on DVI-D
1. The previous version of the Linux driver (7174) was not very strict about maximum pixel clocks over DVI. For me, that driver claims my maximum pixel clock is 400 MHz, so with it you may be able to "just do it".
2. You may want to see if adding
Option "IgnoreEDID" "yes"
helps. Sometimes a new modeline won't be recognized without it.