Well the sanding of the hulls first of all needs to conform with the flow of the water. From bow to stern. Will it make that much difference between 600 and 1600 grit sanding. No it will not, but it may make the sailor faster. Kind of like wet sanding a ACC boat with 1200 every morning before sailing, if they still do that. Psychologically it does wonders. If you think that the boat is faster, it makes you feel faster and therefore you tend to be faster. Awlgrip is the finish on my boats. 600, 800, 1000 then sprayed the top coat. You do not want an absolutey mirror or glass finish on the boat. There needs to be some roughness in the finish. 600-1200 grit doesb this well enough.