I have the same issue.
I run a HDD install on Sony Vaio VPC EB12FX, and with same video chip as yours.
Can't get the video to change more than 800x600...
After a long search and much tries, I got the resolution to change but the video is clearly without the appropriate driver. while you drag a window for e.g it "frames out" or something like that.
this is my xorg.conf atm, just replace yours with this one as we have the same specs.
Section "Device"
Identifier "Configured Video Device"
Option "RenderAccel" "true"
EndSection
Section "Monitor"
Identifier "Configured Monitor"
HorizSync 31.5 - 50.0
VertRefresh 40-90
Option "UseEdidFreqs" "1"
Option "ReducedBlanking"
EndSection
Section "Screen"
Identifier "Default Screen"
Monitor "Configured Monitor"
Device "Configured Video Device"
DefaultDepth 24
Subsection "Display"
Depth 8
Modes "1280x1024" "1024x768" "800x600" "640x480"
EndSubsection
Subsection "Display"
Depth 16
Modes "1280x1024" "1024x768" "800x600" "640x480"
EndSubsection
Subsection "Display"
Depth 24
Modes "1280x1024" "1024x768" "800x600" "640x480"
EndSubsection
EndSection



