5870 and WoW

same....

 

Hate to say this, but you might be much better off playing under VM Fusion using Windows or Boot Camp. Mac versions are known to under-perform the windows client, which IMO is ridiculous but unfortunately true.

 

When I got my Mac Pro a month ago I copied the old folder directly onto the new rig. This resulted in lower FPS than I first expected, and in combination with other problems I did a clean install of everything, including WoW. I downloaded the client from Blizzard. This resulted in much higher performance, the FPS went over 150 FPS immediately when using full-screen mode. Now, I usually only play in window-mode, and this put me back in the 60's FPS-wise which is acceptable for me. I guess I can squeeze it higher by adjusting the settings if I want to.

 

I'm running at 2560x1600 at Ultra settings with 16x multisampling and I get around 30-40 and sometimes as low as 25 or so in Dalaran. In instances it's usually around 70 or so. I also have the quick panning lag but I think that has to do with how fast it can load textures from hard drive.

 

Spank Apple for limiting you to OpenGL 2.0 based graphics and buy a SSD

Windows based WoW uses DirectX graphics which are updated regularly and Blizzard's new Cataclysm expansion has capitalised on this with improved textures, water effects and sunlight.
Mac OS X has received very little love with OpenGL 2.0 being the base 3D graphics platform for games, Blizz uses GLL for its new Mac GFX backend and it just isn't as good. The latest Snow Leopard update improved matters but not enough to compete with the Windows advantage of more recent developments.
If you run the same Mac Pro with a Windows 7 build WoW will work better simply because WoW's GFX backend is optimised for it.
If you insist on using OS X (as I do) your best bet is to invest in an SSD for your primary system drive and put a fresh WoW client install on it too (as I did). This will minimise the texture lag when swinging about wildly in the great wide open.
My 2008 2.8ghz Mac Pro 3,1 with 16gb RAM and Sapphire Vapor-X 5870 runs WoW at 60 fps vsynced with practically no slow down except in Dalaran where it drops to about 30 fps in busy areas or in the trash packs just before Sindi in ICC25 when the AOE goes bananas, the SSD minimises the graphics lag which is dead useful for a melee class.
Hope this helps you out.
Until Apple properly embraces gaming as a major asset, Windows will stay ahead with more mature GFX card drivers and more gamers demanding development relentlessly.
I suspect that as Steve can say "Hey, you can play it in Windows if you want." this isn't going to change any time soon.