I actually think it would be good to have a fat GL. The point of the ring's power is that it is derived from willpower, so it wouldnt matter how fat he is, as he could use the rngs power anyway. However, if he doesnt have the willpower to stay away from the fast foods and the fatty foods, then he wont have the willpower to use the ring. I could kind of imagine Jack Black as being more like kyle than Hal, as Kyle is more of a younger character, and Hal is a military guy (cant imagine Jack Black in the military )