I always understood and Int 3 animal could activate magic items like ioun stones while an Int 2 animal could not. So if all your physical stats are even numbers might as well boost the Int instead.
I also remember playing in the 'good ole days' when you could legitimately play a Int 3 character, so to me an Int 3 animal would be as smart at that Int 3 PC. Most of the 3-Int PCs were played (maybe for comedic value) as rather self-destructive, more often then not hindering the party with their idiocy.