What the drivers do during X startup is detecting what resolutions your monitor supports and then it checks the resolutions and modelines you have in your XF86Config(-4) file. In your case it seems there are a lot of strange resolutions and perhaps unused resolutions in your XF86Config(-4) file.
If you want to remove those errors, remove those wrong resolutions and modelines. (atleast the drivers think they are wrong)
You can also play with the following two options:
Option "IgnoreEdid" <-- Disable probing of your monitor specs
Option "UseEdidFreqs" <-- Forces the drivers to use the horizontal and vertical refresh rates from the monitor section.
These options can make X startup much faster I think.