Surfed a G21 a bit. We did stock plus 2 400s on the floor in main and then a 350 tube sack in the front. Wish we had more, the difference over stock was pretty drastic. Went from meh (for a 100K+ boat) to pretty damn good. We rode just over 11, cant remember exact settings, but those G21s like more weight than stock to get really fun.
Here is a video from a boys weekend with a G21.
https://www.youtube.com/watch?v=Kb5Wa_1EE1s
Also - not that you asked, but for wakeboarding, you dont need anything over stock. that wake is the best stock wake I have ever ridden...