Currently my PSU is a OCZ Fatality 750W PSU ( http://www.newegg.com/Product/Product.aspx?Item=N82E168... ). I don't have any knowledge on PSUs and was always worried that my current PSU was too small or right on the edge of my requirements. I have a friend ready to buy my OCZ PSU so I won't lose much money but don't want to spend the money for a new one if I don't need to. Also if I should get a new one, here are three I was looking at-
Like I said, I know nothing about PSUs or anything like 12V Rails or anything specific. Any recommendations on PSUs or what to do would be great! I would like to not spend the money if don't need to. Also one last question, when i get the 6950s, can running a PSU too small do any damage to any components. Thank you so much and sorry for such a long question.
6950s aren't that much (if at all) more power hungry than 5870s. So if you haven't been having problems with your current PSU, then you shouldn't have problems after upgrading your GPUs.
The OCZ Fatal1ty 750W isn't the best quality unit and only has 650W combined on its 12V rails. 650W is certainly capable of powering a build with two 5870s/6950s, but most people would prefer to get a high quality 750W unit, so I could understand why you would want to upgrade. However you don't need to go up as much as 900W+, unless you are wanting to keep as many upgrade options open as possible.
A pair of 5870's needs about 25 - 30 amps. Figure another 10 amps for an overclocked CPU. That is about 480 watts peak. Figute another 120 watts for the rest of the system and a 750 watt PSU will be operating at about 80% of rated capacity.
A 750 watt PSU will do, but I would put an 850 - 900 watt PSU into a build like yours.
With two video cards, I would not bother with a modular or semi-modular design. You will not have many cables left over.