Help me decide what my weakest link is

I quad boxed D3 some time ago and it ran pretty damn good. Getting ready to quad box crusaders in ROS so I got a new SSD last week and felt the urge to give my system a boost. What would you recommend upgrading if you were in my shoes?

Current Specs

i7 2600k
Asus Maximus V Mobo
Radeon 6970
16GB Ram
256GB Samsung EVO SSD

[MiRai]

At a quick glance I would assume that the GPU would be the first bottleneck, but it's all dependent on the settings you are running. You can monitor your hardware in order to make a more educated guess as to what might need upgrading:

http://isboxer.com/wiki/HOWTO:Tweak_you ... ottlenecks

Using 27inch primary 1920 and 24 secondary to show slaves. I think I capped my slaves FPS to 20-25 last time I played. I just renewed my sub today so I'll get it all setup soon.