I did actually get some good use with them yesterday, defending a hill with them.

The enemy obligingly sent his Halb's and cavalry into my Chiv. Sergeants centre, ignoring my Sword infantry and cavalry on the flanks. The infantry swarmed in from the sides and slaughtered the Halb's, forcing the cavalry general to flee. Meanwhile my cavalry butchered his archers and missile troops and the mass rout was on almost immediately. The result was a comlete butchery of his forces. Over 700 killed/captured to my 30 odd lost.

That was a complete whitewash, and yes, the spears did hold the centre well, but I'm reasonably sure a couple of units of CMAA would have done just as well or very close. I guess I'll just have to try them some more and see. By all accounts though Catholic spearmen before Chiv. Sergeants are a bit of a waste of time except as garrisons.