Manufacturer with Linux support / Screenshot performance / Product recommendation

[volley_ball]

Hi all,

as I am looking for a special feature of a graphics card while running Linux, I had a look at many websites of manufacturers that provide cards with NVIDIA chips. Is it true that there is no manufacturer who officially supports Linux? Concerning my following question, none of the contacted graphics card manufacturers was able to support me.

In order to realize a special HCI application, I need a graphics card/driver/XServer combination which is able to return screenshots (running X.org and KDE/Gnome) in a short time. In order to allow a smooth interaction, a high refresh rate is required (> 10-15 fps, screen size at least 1024x768 pixels).
Currently I am using the methods XGetImage resp. XShmGetImage to get the screenshot. A problem is, that - depending on the video chip and/or driver - the performance of those methods varies heavily. Is there a technical document which contains information on the performance of those functions for current NVIDIA chips?

During my first development, I was able to use a system comprising a NVidia GeForce 7300 LE video chip which already worked quite well. Now I am looking for a new (but not too expensive) video card with a good performance in the described areas in order to complete my new computer. This card should be runnable under Linux using a dual-head configuration (one flatscreen 24" 1920x1200 and a standard projector with e.g. a resolution of 1024x768) with Xinerama extension and - if possible - 3D support. Is it possible to get a product recommendation for this specific case?

Thanks in advance for your help!