I have the same chipset on my laptop with a VGA output.
In lucid the graphics drivers for this chipset were awful - it barely managed 1024x768 at a decent FPS rate. When I connected it to my HD tv it managed 1280x768 (i.e. widescreen) but the FPS rate was shockingly low.
Things somewhat improved with the Natty kernel (available in the software repositories) - from the community wiki:
A few months Canonical has backported kernel version 2.6.38 from Ubuntu 11.04 and version 3.0 from Ubuntu 11.10. Both versions include
the bugfix for the 855GM-problem. It is strongly advised to use one of
these kernel versions because the 855GM-PPA was deactivated some time
Again I managed 1280x768 with a slightly better refresh rate.
A word of warning - take an drive-image backup if you intend to use the newer kernel. It took me a few attempts to get things working - for me I used Stefan Glasenhard PPA (as described in the link) and the Natty kernel to get a stable configuration.
The figures you have been quoted by Intel themselves are theoretical - you will not be able to achieve this on linux with the state of the graphics drivers. Intel themselves are no longer supporting i8xx - the support for i8xx under 12.04 is not known - but given that only VESA support was available in Natty and Oneiric and dont hold out much hope.