The heat dissipated by any radiator system is determined by two things, the airflow and the temperature of the water in the system. Airflow is a result of how fast you run fans, and how noisy that is. The temp of the water governs how much heat is removed by that airflow.

The 1400 watts quoted is with a water temp 15 C above ambient, and likely very fast, loud fans. That water temp and fan speed is in excess of what most water coolers would find acceptable, but it still works.

As Shoggy says in the post you linked a 360 will cool 2 GPU's ... just not quietly and/or not very close to ambient temperature.

So, if you just want to cool your system and don't mind noise then the 720 will do it. If you want to do it quietly, more radiator area is required.

quick google for for your 690's gives ~285W playing Crysis3 (~ 350W each MAX) , for the i7-3960x I assume a 140W package but how much power does it chew when overclocked

Over clocking 3960x to 4.8GHz in this article
http://www.hardocp.com/article/2011/11/1…/8#.UbmS9vkzh9I

it would appear system load is ~350W (~500W @ 4.8G)

So 350 +350 + 500 = ~1200W. In a way 720XT would handle the load, but as you would at peak be getting close to the radiators limit you have to assume you would need a hell of a lot of airflow.


Which as Shoggy article is reflecting YES! you could do it, - but would you want to have such a noisy system?

As Shoogy indicates the 360Xt is for CPU + GPU, and I guess a 720XT is cpu + 2*GPU.

You really have 4 * gpu so for a quiet system will you need to consider "twin towers"

Your heat loads will not be quite that high.
The 690's might draw 350 watts at peak power 100% usage but that would be rare. A 3960X might draw 500W at the wall but the CPU part of that is much smaller. A CPU block on a that chip is unlikely to be getting anywhere to close to the same heat as one of the 690's
If you included a motherboard block the the thermal load would increase but still well short of 1200 Watts of actual heat.