1. A clever nerd wrote an addon which checks if the boss you’re fighting has been parry-hasted.
2. Another clever geek wrote a script which parses logs to determine if parry-haste was seen.
3. Combined conclusion so far is that the only boss in Icecrown with parry-haste turned on is Deathwhisper, and possibly Saurfang.
Read the thread discussing it and download the addon from links within. If you’ve got matlab you can also get the code to parse your own logs. (Nerds ftw).
Data so far suggests that Icecrown raid bosses have parry-haste turned off. It is not conclusive yet.
4. We know expertise reduces parry-haste which is important if Icecrown bosses parried. How much it helps was useful information last week, because I didn’t have the knowledge that mostly ICC bosses don’t parry-haste, yet now the data suggests parry-haste is truly a thing of the past.
5. Theck finalised his analysis on expertise. It was to work out the avoidance value of expertise as a benefit of it reducing parry-haste. Likely, it isn’t important anymore and expertise has returned to only being a threat stat in Icecrown.
The significance of the change for Icecrown raiders is that expertise should be seen as a threat stat (again), so it is not as valuable over the 6.5% cap as I thought last week, which in turn might have implications to your gear choices and gemming in the hard-modes.
That said, the findings have not been fully corroborated yet, but are compelling enough to consider them a basis for decisions now.
If parrygib is irrelevant you can dual-wield with any level of expertise you want. It’s just a threat issue.