How much radiator is needed?

Originally Posted by Electrocutor 

120.2 + 120.2 for a loop with two 7970s and a 3820 probably won't be enough even at stock speeds. It should be fine for normal clocks as long as you keep your water flow and fan speed high, but your deltaT would be really high as well; much more than the target 10 degrees.
You can use some of the results from http://martinsliquidlab.org/2012/04/14/360-radiator-shootout-summary/ as a guideline, but I've not seen any specific data for the EX240. You can expect to get slightly less cooling from a 360 as two 240s.
At stock speed:
210w + 210w + 130w = 550w; + 20w (pump) = 570w
That means without any overclock on the GPUs or CPU, at full load you're looking at almost 600 watts you need to dissipate. At about 2200 RPM, the RS360 dissipates about 280watt and the RX360 about 300watt if you're looking for a deltaT of 10 degrees. That means that even at a very loud 2200 RPM, you would need two 360s instead of two 280s to get decent cooling at stock speed.
One thing to keep in mind is that radiators transfer more heat the higher your delta T becomes, so if you're running instead at a delta T of 20C instead of 10C, your radiators will pull more watts out at the same RPM. Unfortunately, overclocking is dependant on the temperatures of your chips, and a higher delta T means higher chip temps and less overclocking.
[Edit]
The 2200 RPM reference implies that the AP-15 would not be sufficient even at maximum. If you are okay with a high delta T, then you would need more powerful fans unless you get more radiator.

Originally Posted by nleksan 

I would highly recommend looking at a different case, as neither of the two you mentioned seem to be good for water cooling. I would suggest the NZXT Switch 810, Xigmatek Elysium (lower build quality but more rad room than the Switch), a Caselabs M8 (expensive but the CL cases are absolutely the best possible), or similar.
Going by that, I would recommend getting a 420mm radiator and a 240mm radiator. In the Switch, you can have the 420 up top (EX420 w push/pull fans), 240 in the bottom (EX240 Multiport if you want dual-pass options, or Alphacool NeXXos UT60 240), and hang the RX360 off the back. That is what I would do, and with such a setup you're looking at a DeltaT of around 5C give or take, which means massive overclocking headroom and very cool components.
Always get more rad space than you think you need, and never try to squeeze by with the minimum.