1. Depends on the content you're doing, the skill of your entire party, and whether or not you're the MT.
2. I thought the cap was 558?
3. Parry does exactly what it's supposed to do, which is exactly half of what anyone who thinks of stacking it wants it to do. If only we could parry magic... then it would eliminate one situation where it is of absolutely no help!
4. 9 hit zerks are the stuff of legends. If that last hit is a crit BB, threat is never an issue again :P