Custom mode lines don't work with DVI ?

[jsmerritt]

When running my ViewSonic VP201S monitors at 1600x1200 using DVI, I noticed that the "stability" (e.g. jitter/blanking) of the display deteriorates rapidly as the pixel clock rate approaches 162 MHZ. (I am using the on-screen "information" screen built into the display to determine the pixel clock rate).

So, I tried to write custom XF86Config mode lines to reduce the pixel rate. I believe that this should be possible, because when the computer/display is rebooted, the video BIOS (ASUS V9520VS with GeForce FX 5200) brings the console display up at 1600x1200 with a pixel clock of 156.92.

The X-Server accepts my custom mode line and displays the reduced clock rate and associated timing at the very end of the XFree86.0.log, but the on-screen display still reports that the DVI link is running at 162 MHz ... ?

Should it be possible to control the DVI pixel clock rate from a custom mode line or do we lose that capability when switching from analog mode ??? Thanks.