I doubt we'll get an answer.  But I'll throw it out anyway.

 

Any chance of Dell offering the Mobility Radeon X800 XT on the XPS Gen 2?

 

http://www.tomshardware.com/hardnews/20050606_131933.html

 

Tests I've seen at AnandTech don't seem to indicate much performance boost, if any (and if not a loss to the Ultra).  But it will use 35 watts vs. 65 for the Go 6800 Ultra.  Definitely help battery life.