Alright, I've decided Synchronized Strike and Synchronized Defense are definitely in, the question is, which version of Strike should I use.

Synchronized Strike: Getting hit by one partner in Melee provokes an attack of opportunity from the other (AKA, meatgrinder as they pass the AoO's back and forward.
Synchronized Strike: Getting hit by one partner in Melee provokes an attack of opportunity from the other once per turn. (Still pretty nasty when combined with defense, but the "Pass" can only happen once per person. So it's Partner A Gets hit, partner B AoO's, triggering Partner A's AoO, which triggers another AoO from partner B (his first one was triggered by Synchronized Defense, so it didn't count for his Synchronized Strike that round).
Synchronized Strike: Getting hit by one partner in Melee provokes an attack of opportunity from the other. Getting hit by an Attack of Opportunity does not trigger this (Okay, Now they can't pass AoO's anymore, but expect to see some nasty Greatsword and TWF combos as one partner Full Attacks, triggering AoO's for the other.
Synchronized Strike: Getting hit by one partner in Melee provokes an attack of opportunity from the other once per turn. Getting hit by an Attack of Opportunity does not trigger this. (Okay, this was what I origionally intended, but I'm not sure how much I like it. People have been saying the class is underpowered, and an AoO-ping pong may be an effective way to handle that).