So I was messing around with raidbots a little, comparing the spec score of Top 100 logs vs. the spec score average in 25 man heroic.
I chose 25 man heroic because it's safer to assume all buffs/debuffs are covered.
The spec score (www.raidbots.com) basically compares the performance of each spec compared to the top performer that given fight (who's defined as 100%), and is then scored depending on how well it did. So a spec doing 90% of the damage of the top scorer, will get a spec score of 90 for that fight.
I'm only mentioning this because the spec score for the Top 100 is actually lower than the Averages, which indicates that in the Top 100 fights, you'll often have one spec outperforming others by a large margin (possibly artificial boosting to score a ranked position).
Anyhow, that said, I got some interesting results.
Frost Death Knights, followed by Fire Mages and Balance Druids had the lowest deviation between a Top 100 performer and an Average spec score, while Unholy Death Knights, Subtlety Rogues and Arms Warrior had the highest deviation between the two. (BM and FM not accounted for)
What does this mean? If I understand it correctly it means that the (heroic raiding) Arms Warrior performs better, on average, compared to other specs. Ergo, while an Arms Warrior in a Top 100 log is far behind the top scorer in most cases, on average he's quite competitive.
So it could say as much as the average Unholy DK more skilled than the average Fire Mage or Balance Druid.
Anyway, feel free to mess around with the data: http://raidbots.com/dpsbot/Spec_Scor...default/#3vvft