faster memory cards help but doesn't mean it won't slow down as camera buffer rate and memory card speed plays a part. CF card may be faster than SD card.
and also shooting RAW affects greatly,so JPEG and smaller file size will help as well.
I've shot RAW+JPG onto a standard 90mb/s SDHC card and it didn't slow down for at least 10 secs. This video is 5 secs long WITHOUT any card and yet it slows down very quickly. Therefore the camera must rely on the card to a large extent to maintain buffer throughput.