I've been playing the WoW stress test this week. I leave the FPS counter on most of the time and twice yesterday i noticed my fps slowly dropping from about 70 fps all the way down to 3 fps when there was nothing special going on on the screen.

My first instinct is that my overclocked video card was overheating or something. Is this a symptom over an overheating video card?

What do you mean by "nothing special going on"? Are you referring to duration when the game is loading? When a game loads there isnt gonna be a lot of frames since the screen is pretty much static besides the loading bar.

I mean i was just basically standing still, nothing was loading, no group of players coming out of no where. It was very different from any sort of framerate slowdown i've seen in the past. It was gradual over the course of about 45 seconds.

Video slowing like that is usually heat related. Since you are OC'ing the video card the stock fan may not be strong enough and the card is overheating. Try taking the side panel off the case.