Just received my new Canon S70. Want to order larger capacity memory for this camera (>= 1GB). I've looked in the Canon documentation but haven't found the spec's for maximum speed for CF cards. Since there are many speeds available (ie, 20X, 40X, 60X, 80X, 100X, etc.) I don't want to buy one that is faster than the camera can accomodate since higer speeds equates to higher cost. How does one determine what the optimum speed CF card is for this camera? What is the optimum speed CF card that this camera can use?