can anyone tell me the diference between the ko 407s, 408s, and 409s receivers i race igt stock slash and vta cars my reflexes are slowing down and i can't keep up with the younger groups but still enjoy racing what is recomended for someone like me i currently have an ex1ur with 408s receivers but i see that they are discontinued but i still need a couple of receivers for the cars any help would be appreciated thanks