So unless you NEED to have an iMac, I'd recommend getting a Windows PC
For the price of 27" iMac, you could get absolute top-end gaming PC with 27" IPS monitor
Yes. It always tears me heart up a little inside to see gamers paying a $500+ markup on laptop hardware (because the GPU inside there is designed for a laptop, hence the 'M' affix.) For $1500 you could tear through anything you play on a PC.
Funny you mention $1500 because this is what my new 27' iMac with a GTX 680mx will cost me. The thing is my old late 2009 imac has been sold for $1500 and my new one will cost $3000 with the 680mx, the 1TB Fusion drive, 3 years applecare and sale tax.
The difference between a PC and a MAc is a 3 years old PC would have been sold for maybe 300$. The Macs have great resale value. So I am not really paying more than a PC.
Ok back to the topic subject, here are the benchmarks for various iMac GPU mixed with desktop GPU's (3DMark11 P GPU)
4 NVIDIA GeForce GTX 680 - 9861
7 NVIDIA GeForce GTX 680MX - 7352
16 NVIDIA GeForce GTX 570 - 5033
17 NVIDIA GeForce GTX 480 - 5014
22 NVIDIA GeForce GTX 675MX - 3978.5
25 AMD Radeon HD 6870 - 4218
26 NVIDIA GeForce GTX 470 - 4267.5
32 NVIDIA GeForce GTX 675M - 3248
33 NVIDIA GeForce GTX 580M - 3131
55 NVIDIA GeForce GTX 660M - 2320
61 NVIDIA GeForce GT 650M - 2085
73 ATI Radeon HD 4850 - 1780
82 NVIDIA GeForce GT 640M - 1719
209 Intel HD Graphics 4000 - 524
So the base 27' iMac comes with the NVIDIA GeForce GTX 660M, which will give pretty decent WoW performance considering its better than my Radeon 4850. But don't expect to be able to play with Ultra setting and Max out view range. The iMac with the NVIDIA GeForce GTX 675MX is a much better GPU choice and would allow to play with everything max out.