The Quincunx is the ONLY formation i use if playing with romans (pre-marian) it works quite well, because once the enemy gets tired from fighting the hastati, they get charged by fresh principes while the hastati withdraw. this causes many a rout. Even more so when i upgraded to polybian.

Only thing i am wondering about is what to do with the hastati once they have withdrawn, done an about face to fill the place where the principes were, and get all rested up. do i rotate the princs back and re-charge with the Hastati, or Flank? I dont really use my triarii, because from what i read, triarii were only used in bad situations. Most battles where i did use the triarii i had Extrordinarii to support them, so the combo of both units usually ended up RIPPIN SHIT.