Well i look at how well gibbs did with the deccan chargers, i also know if gibbs gets going he is capable of far more destruction upfront than kallis. JK remember that we need to keep momentum, Players can get injured while training just as much as they do during a cricket match.
I don't think resting players is a great idea in pro 20 because its so short why rest players? Keep a team playing together and make sure they all know they will start the next game because you want confidence, you don't want players thinking this may be their only chance to get into the next game, i dunno if that makes any sense