Here's a picture of my screen after trying to change the resolution.

Here's my xorg.conf. I've tried with and without the custom modelines for 1680x1050@60 and 1440x900@60 and also using the default refresh rates vs the correct ones below obtained from manufacturer documentation. All configurations have the same result.

Section "Files"
        FontPath        "/usr/share/fonts/X11/misc"
        FontPath        "/usr/share/fonts/X11/cyrillic"
        FontPath        "/usr/share/fonts/X11/100dpi/:unscaled"
        FontPath        "/usr/share/fonts/X11/75dpi/:unscaled"
        FontPath        "/usr/share/fonts/X11/Type1"
        FontPath        "/usr/share/fonts/X11/100dpi"
        FontPath        "/usr/share/fonts/X11/75dpi"
        # path to defoma fonts
        FontPath        "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
EndSection

Section "Module"
        Load    "bitmap"
        Load    "ddc"
        Load    "dri"
        Load    "extmod"
        Load    "freetype"
        Load    "glx"
        Load    "int10"
        Load    "vbe"
EndSection

Section "InputDevice"
        Identifier      "Generic Keyboard"
        Driver          "kbd"
        Option          "CoreKeyboard"
        Option          "XkbRules"      "xorg"
        Option          "XkbModel"      "pc104"
        Option          "XkbLayout"     "us"
EndSection

Section "InputDevice"
        Identifier      "Configured Mouse"
        Driver          "mouse"
        Option          "CorePointer"
        Option          "Device"                "/dev/input/mice"
        Option          "Protocol"              "ExplorerPS/2"
        Option          "ZAxisMapping"          "4 5"
EndSection

Section "InputDevice"
        Identifier      "Synaptics Touchpad"
        Driver          "synaptics"
        Option          "SendCoreEvents"        "true"
        Option          "Device"                "/dev/psaux"
        Option          "Protocol"              "auto-dev"
        Option          "HorizScrollDelta"      "0"
EndSection

Section "Device"
        Identifier      "Generic Video Card"
        Driver          "ati"
        BusID           "PCI:1:0:0"
EndSection

Section "Monitor"
        Identifier      "Generic Monitor"
        Option          "DPMS"
        HorizSync       31.5-91.1
        VertRefresh     60-100
        Modeline        "1680x1050@60" 162.00 1680 1704 1792 2136 1050 1201 1204 1249 +hsync +vsync
        Modeline        "1440x900@60" 162.00 1440 1464 1552 2136 900 1201 1204 1249 +hsync +vsync
EndSection

Section "Screen"
        Identifier      "Default Screen"
        Device          "Generic Video Card"
        Monitor         "Generic Monitor"
        DefaultDepth    24
        SubSection "Display"
                Depth           1
                Modes           "1920x1200" "1680x1050@60" "1440x900@60" "1400x1050" "1280x1024" "1280x800" "1152x864" "1024x768" "800x600" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           4
                Modes           "1920x1200" "1680x1050@60" "1440x900@60" "1400x1050" "1280x1024" "1280x800" "1152x864" "1024x768" "800x600" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           8
                Modes           "1920x1200" "1680x1050@60" "1440x900@60" "1400x1050" "1280x1024" "1280x800" "1152x864" "1024x768" "800x600" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           15
                Modes           "1920x1200" "1680x1050@60" "1440x900@60" "1400x1050" "1280x1024" "1280x800" "1152x864" "1024x768" "800x600" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           16
                Modes           "1920x1200" "1680x1050@60" "1440x900@60" "1400x1050" "1280x1024" "1280x800" "1152x864" "1024x768" "800x600" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           24
                Modes           "1920x1200" "1680x1050@60" "1440x900@60" "1400x1050" "1280x1024" "1280x800" "1152x864" "1024x768" "800x600" "640x480"
        EndSubSection
EndSection

Section "ServerLayout"
        Identifier      "Default Layout"
        Screen          "Default Screen"
        InputDevice     "Generic Keyboard"
        InputDevice     "Configured Mouse"
        InputDevice     "Synaptics Touchpad"
EndSection

Section "DRI"
        Mode    0666
EndSection