WoW: Ideal 3s (Ultra settings) GPU question

[MadMilitia]

Right, so lets get to the system specs as they are today.

Case: Antec 900 ATX Mid tower
CPU: i7-2600K CPU @ 3.40GHz
RAM: 16 GB DDR3 dual channel
GPU (Current) NVIDIA GeForce GTX 460 2GB
DISK: Intel SSD 120GB
PSU: Some thermaltake 1100 watt I believe.
MB: Asus P8Z68-V
OS: Windows 7 Ultimate


My GPU question:

I want to add an additional monitor to expand my desktop from 2 * 1920 x 1080 to 3* 1920 x 1080. I also want to be able to run my 3s team on something higher than fair settings. High if possible, ultra would be great but I realize that may be an issue. I have zero interest in adding more WoW instances. 3 will be all I run anymore.

What is the best GPU for this? Something high in vram I assume but does it need a lot of calculation power? I did at a time run 2 of these 460 GTX cards but I gifted one of them to my brother for the holiday (he also plays games) so I'm looking to replace the card but want to be sure that I'm spending wisely. My budget? I could do about 500USD for just the GPU. I'm just going to get a standard 60hz 1920 x 1080 to complete my screens at another time.