Comment 120 for bug 349412

Looks like 16x10 on the 23" panel uses a higher dotclock; it's not a reduced blanking mode:

good:
  1680x1050 (0x44) 119.0MHz +HSync -VSync *current +preferred
        h: width 1680 start 1728 end 1760 total 1840 skew 0 clock 64.7KHz
        v: height 1050 start 1053 end 1059 total 1080 clock 59.9Hz

bad:
  1680x1050 (0xb6) 146.2MHz -HSync +VSync
        h: width 1680 start 1784 end 1960 total 2240 skew 0 clock 65.3KHz
        v: height 1050 start 1053 end 1059 total 1089 clock 60.0Hz

The 1920x1080 resolution on the 23" looks like it's reduced though:

  1920x1080 (0xb4) 138.5MHz +HSync -VSync +preferred
        h: width 1920 start 1968 end 2000 total 2080 skew 0 clock 66.6KHz
        v: height 1080 start 1083 end 1088 total 1111 clock 59.9Hz

I wonder if the Windows driver squeezes the htotal/vtotal down even further though, reducing the pixel clock requirements a bit more...

If you want to run 16x10 on the 23", you could try adding a custom mode using the output of cvt -r 1680 1050, and using that in your config instead of the EDID provided mode.