Hi-
You can have Quartz Extreme support without Core Image support, but any card that supports Core Image also supports Quartz Extreme.
They are not the same thing.
http://en.wikipedia.org/wiki/QuartzCompositor#QuartzExtreme
http://en.wikipedia.org/wiki/Core_Image
Quartz Extreme is a basic necessity for any OS X prior to Tiger, and is still a necessity for GUI functions, as well as many softwares today.
Quartz Extreme leverages the GPU via OpenGL.
For better Quartz Extreme support, later version support for OpenGL is necessary.
Even without Core Image support, proper OpenGL support is necessary for proper application function.
Tiger needs support for OpenGL 1.5.
Leopard needs support for OpenGL 2.0.
Core Image is a more modern use of the GPU for offloading previously CPU intensive tasks.
Core Image support is recommended for Tiger, but should be thought of as required for Leopard.
No Radeon card lower than a 9600 series card supports Core Image, and no Geforce card lower than the 6200 series
properly supports Core Image.
PCI graphics in an AGP machine +is not+ a performance option.
The only reason one would want a PCI graphics card in an AGP machine is to connect additional monitors, with the understanding that advanced feature support would be absent.
Even though the 9200 PCI can be hacked for Quartz Extreme support, it can be a highly problematic card, alone or otherwise.
http://www.xlr8yourmac.com/Graphics/macradeon_9200pcitests.html
http://www.xlr8yourmac.com/osx/quartzextreme_pcimod.html
Even with a hack, many apps will not see the card as supporting Quartz Extreme.
Besides, the best OpenGL support a 9200 can do (PCI or AGP) is OpenGL 1.4.