The only cap on how fast you can swing is how fast you can press the button with default Graal. On PC Graal, you can swing extremely fast by pressing the key you use for sword and then holding Tab (chat bar). Holding Tab makes the chat bar open and close and when it closes your sword will swing. Doing that lets you swing every frame, or 20 times a second. Of course, the only thing this is good for is laming because you can't move while doing it.