The latest cards do not include dedicated 2d chips anymore, and so they are uniformly slower in 2d than even 15 year old S3 cards.
Nvidia 7xxx or below, and Ati X1xxx and below still have dedicated 2d units.
Only from the same vendor currently, ie another Nvidia.Will Ubuntu "just work" if I added a 2nd video card to a free PCIe slot (I have a crossfire-capable mobo)?
Depends on who you ask. They are about equal in the latest series.Would AMD cards work any better?
No, they are 3d techniques.Would Crossfire or SLI help 2D dual monitor performance?