Well Quick, I have been playing for 2 1/2 hours at 960 with no real issues. 2560 x 1600 on my dell 30" and FRAPS telling me 41.8 FPS avg over a 60 second bench pull on a random map.
Now that I am deaf from the 100% fan I can go back to normal mode
Something is up if you can't hit 900MHz with a 1.1v which is what I am running for the 960MHz and further that you have to up the voltage to keep them stable at factory. It makes me almost wonder if something is up with that OCZ PSU. Crazy idea, maybe yank two of the cards out and let them just hang on your WC loop with no power and see if you can get one of them to OC to 960+. That might tell you it is either something with your MOBO or something with the PSU. I would say you might have a bad card, but 3 of them is no way. Maybe change the utility you are using to OC, did you use precision or something like Tweak GPU?
Also on those classified they have voltage reading points on the back, so maybe you should break out a multi-meter and see if the software is reporting correctly.
I guess my best advice would be to start with one and see what you can do with it to figure out if it is the card or something else in your system that is limiting your OC. You have more than enough cooling as the 480 and 360 should give you around 1700 watts of cooling and those 3 cards are only putting out about 750 watts OC'ed. A single 480 rad would probably be enough but why not
Sweet rig btw, I just upgraded mine to an i7 2600k on a MSI z68 board that is running an EK Nickle HF on the CPU and looking to grab a Koolance or Heat Killer hole addition for the GTX570. I have an XSPC RX360 rad, and 120MM Feser rad (was a gift) in my loop. The rest is Corsair 850W PSU, 16GB Vengence memory, and a Corsair 700D case. I was thinking about grabbing a case labs case as my next upgrade but the way my desk it set up I am not sure it would fit. They are SWEAT water cooling cases. I had an EK block on my GTX470 but like most people the nickle plating started wearing off and the copper showing through.... not good.
Let me know how it goes, very curious why you are having so much trouble and it was cake for me.