Well, I thought I'd post an update with everything I learned.
I loaded WOW on my Windows XP Boot Camp partition, and it works beautifully. With the shadow detail on low, I get an average of 70 fps with no slowdown over time. In fact, no matter how hard I tried, I could not get the frame rate to dip below 50, which is a world of improvement over the OSX side. For some reason, I'm not getting the same wild frame rate fluctuations that I was getting on my OSX partition. On my mac, my fps would be 120 one minute, and drop to 27 the next. On Windows, it's a much more solid performance.
So, that must mean that the drivers on the OSX side are subpar, which is actually a relief. With some of the other overheating nightmares I'm hearing about, I consider myself lucky. It saves me a trip to the Apple store, and much wasted time. Also, if the computer had been overheating due to a botched design, there would have been no solution to the problem at all. I'm sure Blizzard will update the drives with time, so until then, I'll just play it on the Windows side. A necessary evil, I guess.
Thx for your update. Great that you have sorted your problem.