Re: Best nvidia card for video playback on Linux?
The best is properbly the 7800 GTX-512, but the best you can afford. Any GeForce 6600/6800 or 7800 card should do, especially if you have it in an PCIe slot - which I assume is not available to you unless you get another motherboard. I haven't tested any of those cards though, but if you can afford it, I would go for a 7800 GT or higher. The 7800 GT costs about the same (or less) as a 6800 GT and has a lot more to offer.
Anyway, don't you think this is the wrong place to ask? This is a Linux forum, but the question you are asking has very little to do with linux.