Optimal bat size/weight for 13yr old

I realize that bat size is a very individual decision but I would welcome any thoughts or advice on this subject. My son will soon turn 13. He is fairly big for his age - ~5'9", 175lbs and in good shape. He currently plays for an Optimist Sundowner select team. He is using a 32"/24oz bat for games and seems to like it alot. He has quick hands and has had no problem getting around on the ball. He has also been using a 32"/30oz wood bat for batting practice. The wood bat saves wear and tear on the aluminum bat and, I believe, results in greater bat speed when he steps down to the lighter bat for games. I am trying to weigh (no pun intended) the pros and cons of moving him to a heavier bat for game use, perhaps a 32/29 or 33/30. These numbers are in line with charts I have seen. He will be entering 7th grade next year so high school ball (and the -3 bat requirement) is still a ways off - spring, 2004. I happen to subscribe to the "lighter is better" school of thought as long as the bat isn't too light. I don't feel a great need to push him to a heavier bat right now unless a good argument can be made that it would be to his benefit. Does anyone have a good argument?

Thanks for your feedback.