playBunny: I agree that doubling requires a different way of thinking, but in your original post you mentioned additional skills. Yes, it takes additional skills to attack a king that has the ability to castle over one that can't in the rules. This imbalance is exasperated in Fischer and CRC, where no set starting position exists, but castling and the ability to prevent it plays a far more significant role than in conventional chess. I've personally found that in CRC and Gothic/Janus chess, due to the width of the board, castling can significantly alter the course of the game by necessitating a redirection of the attack. Of course the cube requires additional skills too, but you're still playing backgammon!