What will you be using the monitors for? Gaming?
Also, at what graphics settings are you planning on planning on? High/Ultra?
The reason is the amount of VRAM you may need. The 7970 3GB will suit those needs. The power of the GTX 670 is strong enough to handle multi-monitor gaming but you would probably at least anything higher than 2GB of VRAM. It's just dependent on how much you want to spend. If you want the best bang for your budget the GTX 670 is the best.
since there new video cards i would prefer my settings to be on ultra. The monitors will be used for gaming and also doing random stuff such as surfing the web, watching movies and stuff like that for everyday usage.
So will gtx 670 sli be better for 3 monitor setup. And i would like to know ur opinion on which is better Eyefinity or Nvidia surround?
Well, if you get a GTX 670 4GB it would be preferred. Both are good setups. Performance is only limited by the graphics card. AMD needs a displayport adapter to use, while the Nvidia Surround needs to use an SLI configuration for multi-monitor setups. But, that has changed.
Now, they both can run more monitors on one card. Either one is not better than the other.