Well, I still wonder, if "streaming in low fps" is the same as "a low framerate video capture". If a captured video can be "restored" to a higher fps video, it would be fine. Another question is; is it possible to get more fps/quality if you focus to cap the upper screen only than both screens at the same time?
Yeah, capture cards are in general better than other methods, but for me its more like "I can capture the 3ds screen w/o a cap card??? Hell yeah!" than the actual need of capturing it for a direct purpose.