OS X Sudden WoW Frame-rate issues

Hey folks -

So I hadn't played WoW for a few weeks due to business travel and Christmas etc.

I fired it up yesterday to find that when logging in everything is OK the first time I login for about 30 seconds. Smooth graphics, 100+ fps, no problems. Then my FPS tanks to the mid 30's and there's a noticeable stutter as I move around. This just started happening within the last two or three weeks.

I already tried disabling all add-ons and that didn't help. Has anyone else experienced this recently? Here's my specs:

Mac Pro 5,1 (mid-2010)
2.8 GHz Quad-Core Intel Xeon
32 GB 1066 MHz DDR ECC
ATI Radeon HD 5870 1024 MB

Display: Asus VH232H running 1920 x 1080

Mac OS and WoW both sit on Samsung 840 SSD's.

I can't believe this is a power issue. This thing boots in 12 seconds and loads 100 GB Aperture libraries instantly.