My experience is that flanking with melee troops (even cavalry) isn't nearly as effective as with skirmishers. I've seen (admittedly more elite) units in phalanx formation holding out for very, very long while they were completely surrounded with Principes. Multiple charges with cavalry will start resulting in heavy cavalry losses, so that's not a sustainable option.
My current tactic with hoplite formations is fixing all hostile melee units in place with infantry, taking out their ranged troops with cavalry, and then flanking the hoplite formations with skirmishers. Pila in their backs do wonders.