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IIRC the Dual 2.5 GHz G5 uses AGP 8x for video...

Two cards spring onto mind:
- nVidia GeForce 6800 Ultra
- ATi Radeon X800 XT Mac edition
 
ATI Radeon X800XT Mac Edition - hard to find since it's discontinued.
ATI Radeon X850XT OEM Mac card - hard to find because it's an OEM card.
Geforce 6800 Ultra or GT OEM Mac card - also hard to find since it's OEM.

By the way the ATI Radeon cards mentioned above offer only one dual-link DVI port whereas the Geforce cards offer two dual-link DVI ports.
 
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