Display cards don't improve the picture quality (they may help on playback, but only when useing power dvd or any other player). The card handles the overlay and it affects the video depending on the settings u use but only for display purposes, your main output is not affected (and can be tricky for color correction unless u have a good lcd monitor).
Your capture device and selection of codecs is what actually affects quality. In fact, 1394 I/O though an standard, is the poorest capture way (in terms of professional/boradcast quality).
Both cards are pretty similar in performance... I wouldn't worry that much unless you plan to add editing hardware, if that's the case u should check compatibility.