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While this is no real benchmark, I just finished playing WoW on the new 20" iMac w/HD 2600.

I maxed every setting and enabled every effect at 1680x1050 and the game played extremely well.

My FPS usually hovered around 55-60, although I noticed it dip to 30 during a flight path.

I'm a level 26, so I can't check high level raids, etc.
 
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