James,
I am not Casper but a pretty close replica, lol. The GTS will, to the expert racer, feel a little morre punchy but still be a little smoother on throttle. Most folks using the two will not feel the difference. They are both pretty good ESC's and if one is already installed ina machine and you have a machine sitting there that has nothing in it, put the new esc in that one. Or, if you want to make your son really happy, put the new one in his, haha.