Graphics Card - G5 upgrade

Hi guys,

I'm looking to upgrade from my ATI Radeon 1900 (128mb Vram) grfx card in my Dual 2GHz G5.

I have seen the following cards: ATI Radeon 9800 Pro, ATI Radeon 9800 XT and Nvidia GeForce 6800 GT.

Can anybody please tell me which would be the better card for my mac? I have never upgraded my grfx card before and could do with a few pointers.

Cheers,
Mat.