It's not that frost DK's are OP its a scaling issue that they get higher DPS alot earlier than unholy. It's alot like paladin's doing 1.2-1.6K at level 60 which is alot more than any other class but then it all levels back. A frost DK at level 60 (I am raising a new one to plot DPS at lower levels) only does 400-600DPS because we don't have howling blast.
Unholy are definitely doing more damage in the higher gear bracket but they need the gear to pull it off. Given that why would blizz nerf frost DK's .. enjoy the fun :-)
Basically I would say if you are a DK and don't have access to raid gear you probably should be in frost. I really hate gearscore but GS terms thats sort of 4700-5600 and assuming normal Justice point gear. There is a massive difference between frost and unholy DPS at this gear level.
** Remember Warcraft players fail in directions you never thought possible.
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