All I have with me on the boat is 320 and 400. I tried using those two out today and I cringed with how scratched up the arm got with 320...but I finished it and went to 400. After going over it with 1500 a couple of times then wetsanding it I was pleasantly surprised at how well it turned out! I also tried a new method with applying the mothers polish. I put the tip in the polish on low speed to give it a light coat. I then applied the polish like normal to the arm with a microfiber cloth. It seemed like it did a much better job than just putting the polish on and using a fresh tip. Thanks for the advice all rice.