I just compared my 2 SGs, one with 18 RB and one with 42 RB. On a rebound per full game, it looks like the diff between 18 and 42 RB in a SG is about 1 RB per game. Not very scientific, but that seems to be the way it feels. Some guards with a 2 RB still get 1 a game just by quickness and long rebounds.