I read something on the Blizzard boards about how there is a documented problem with the latest WoW Patch (1.8.1) and ATI cards. They're allegedly working with ATI and Apple actively to fix the problem. We've also had misaligned text in our "Guild" tabs for about 2 months now so the degree to which Blizzard QA cares about this stuff is hard to imagine.

I have an original iMac G5 and I've wrestled with the various video settings for some time now. A few things I've noticed to help performance:

-Disable Vertical Sync. It doesn't help at all. Unless you have horrific screen tearing I say live with it and enjoy the FPS.

-Disable Smooth Mouse. This is also known to be a FPS killer on the Mac.

-Don't use any shader options. Pretty much anything down there is going to result in a tremendous performance hit.

I also set Terrain Distance to Medium and Texture Quality to Lowest. You've got a lot more horsepower than me though (single processor G5 1.8GHz and an NVIDIA GeForce GO) so you may be able to toy around with that a bit.

Also, since you're running 10.4, be sure to go to System Preferences ---> Spotlight and include your World of Warcraft folder as a private folder not to be indexed.

Hope some of those tips help.