iMac graphical World of Warcraft lagging

Recently I noticed a significant drop in graphics performace while playing WoW. I'am currently using a 27 in iMac (Mid 2011) with 3.4 i7 and the AMD 6970m 2GB graphics.

We all know that WoW is not very demanding when it comes to graphics. But I noticed serious lag in battlegrounds, instances and even in the open world. When the lag starts it causes the application to completely freeze and even cause the think wheel to appear. After a short while the game responds and catches up. This issue repeats itself for a little while.

So far here are a few things I have done to attempt to remedy the issue.

According to some suggestions on the blizzard forums and tech support. The following has already been completed.

-Restarted modem and router

-Tested game on different user enviournment

-Tested game on different OS

-Uninstalled and Reinstalled WoW

I also came across and interesting read on third party forums about the potential REP for these inparticular graphics card but I have no had any graphical distortion while playing and also did not have any graphical issue outside of the game.

any suggestions as what i should do next?