I'm no video card expert (Mouse is your man for that) but I do know that the more powerful the card the better for what you want to do. It is also a general rule that the more you pay the better the card so I suppose the decision comes down to how much you think it's worth paying to do what you want. You also need to make sure you've got an appropriate slot on your mother board. Most top quality cards these days are PCI-e and whilst the slot looks exactly the same (see picture) they are not compatible with the earlier PCI standard.
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Do you know that we're all in line for succession to the throne? Really?
Well, if forty-eight million, two hundred thousand, seven hundred and one people died I'd be Queen.