maybe this doesn't make a difference, but aren't a thumber and a tomahawk a different shot? Thumber has thumb inside rim with the flight plate away from your body, the tomahawk had your fingers inside rim, with the flight plate towards the body. I'm just thinking that you really can't compare a forehand to a backhand as exactly reversing the same shot in terms of ideal weight and stability of a disc because there are inherent differences in the spin, and release between the two shots. I don't throw many overhand shot, but I'm assuming that there are many other subtle differences between tomahawks and thumbers that make disc selection just as different as it would be for forehand vs backhand.