Paddling at a higher speed will incorporate too much air and will cause your cookies to spread. There is a specific technique to piping langues de chats. Hold your pastry bag at a 45 degree angle from the surface. Squeeze the bag and draw down 1 inch to form a cookie. Stop squeezing and make a quick and sharp upward movement with the bag to "cut" off the batter. There should be a tiny tail of batter towards the top of the cookie.