Can't talk to you about raid, because I don't raid, but on my 24" 3.06 GHz iMac with 8800GS video, with all setting cranked up, no full screen glow, I get well over 60 FPS at pretty much all times (even over 200 FPS often while testing, but I keep the rate capped at 30 anyway). You'll definitely get over 60 fps in cities (I haven't tried it in Dalaran, but in Orgrimmar, Stormwind, and Ironforge that's the case).
However, something about the Wrath of the Lich King expansion makes it occasionally glitchy. Not horribly so, but it happens and can drop the frame rate briefly. I *think* this is a Mac and/or video driver issue that they need to fix, and I've seen many people complain about it in forums. That's with oversampling cranked up, if I turn that off it still looks good and the frame rates can go even higher. Anyway, I don't think you'll be disappointed with the 8800GS model.
That said, you may want to wait a bit because I think the iMacs will be updated before too long, maybe with LED-backlit screens.