... really ants the size of apples would be enough of an improvement to give us a run for our money. Especially factoring in the increase in intelligence given the larger number of mushroom bodies in an hymenopteran style brain of that size.
The brains of eusocial insects are mysterious for their small size, they do more than seems possible with so few cells. So what happens when an ant has a brain the size of a mouse? But with ant architecture?