I believe that DVI to component cables only work for cards that support them (ie can do component out via a DVI connector). If your card does component via its own connector, then I assume that it does this instead of being able to do component via a DVI cable.
I would imagine the quality through your dedicated cable would be the same as a card that does DVI to component. That being said, if your TV has a DVI cable already on it, then you could go DVI to DVI!
/bill