That is a VERY old rad, flow restictive and way less capable than newer ones.
Spawn gave you a great starting point. How do we know these things? Scientific tests at Martins and Skinnees. Might want to take a gander at this link and use the links within big time. You got till summer, so learn a bit.
http://www.tomshardware.com/forum/253958-29-watercooling-guide
If your going to add GPUs you might want to think about fatter tubing. You'll need more flow rate for the best performing loop adding GPUs. Also, you'll probably need more rads depending on your GPUs, so might think of more rad now. As your sig is now, adding a GPU you WILL need a 120x3 sized rad depending on your overclocks. So plan ahead.
You need a 120x2 for your CPU now. Adding GPUs makes your Delta T worse.
Simple explanation of what DT is, YOU NEED TO UNDERSTAND IT.
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DT Temps
A delta measurement is used in many engineering terms in many disciplines. I guess it means the difference between two of the same thing.
In water-cooling it's simply the difference between the ambient air temps and the water temp on the outgoing side of the rad. Room temps vs. water temps. A better rad setup cools better. Load meaning heat created. Stable meaning the load has been running long enough so the loop is stabilized, heat is made; it is removed and run long enuff for the water temps to get to the max under a load.
If your ambient are 60C and your water exiting the rad is 65C, you got a 5C DT. And it’s important you understand this simple concept. You need xx cooling for xx heat load with a resultant xx DT. Its how you decide what size radiators you need as a minimum for the loop to perform better than air, and what’s needed for really superior max over clocks.
So for example, in a water cooled loop you generate 200 watts of heat. Your block pulls heat into the water; the heat is dissipated into the air by the rad/fans. Skinnee and Martin came up with a great chart for rad test results. Make xx heat, run xx fans with xx radiator brand and size, your DT is xx.
The efficiency of the rad determines the residual heat in the water as it circulates. A rad cannot remove ALL the heat. Heck if that was true, running a rad with no heat load would cause the water to go all the way down to below freezing theoretically. A great Delta T is under 5C, meaning you got a big rad for your heat load. Medium DT is 10C, and 15C is getting bad. CPUs need lower DT than a GPU loop.
Ultimately lucky folks with cooler temps year round can go with lesser rads. People with high ambient might need bigger rads for the same final core temp on a CPU that someone in Norway vs. Samoa can get.
Hope that helps, it's a simple explanation, I'm not a Thermodynamic engineer.
