Can I give you a prep on wattage generated vs wattage removed?
A short answer is a good 120x2 with medium speed quality fans is enough. A 1 Ghz bump, hmm it might be possible depending on your chip, cooling system, motherbaord and your knowledge in overclocking.
A place you should bookmark is:
http://www.skinneelabs.com/
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 ambients 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 for 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.