My son has outgrown his RBZ's size 4.5d (toes touching the toe cap). He tried on a 5.5 Super Tacks and while his toes were not touching, they fit like a glove but he is still growing. I know u can't say for sure but what is your gut feeling of the size he would need in either the Tacks or Ultras? I need to get some time out of them without going too big, as he is growing like a weed, LOL!