Originally Posted by ronaldinho07
Yes,maybe its my problem,trying to turn the block around,..then GPU 4 is still hotter than the others but temperature increase slowly
That sounds more like your flow issue where your pump is simply not moving enough water and/or your fans are not running high enough to dissipate all the heat. The 7970 has a TDP of 250 watts, so you'll need your fans moving a good bit of air to take care of all that and your flow rate will need to be high enough to keep the heat spread out across the water. From your pictures, it looks like your 720s currently have push-only fan setup; having push/pull does help quite a bit especially if your fans' static pressure is somewhat low (I can't tell what fans you're using).
From the components you have shown and a better pump, the optimal setup would be:
D5 Pump (or 2) -> GPU0 | GPU1 -> 720 rad -> GPU2 | GPU3 -> 720 rad -> GPU4 | GPU5 -> 720 rad
36 fans in push/pull configuration at a moderately quiet speed or 18 fans on nearly full blast
In a normal case, that would be overkill for radiators (giving each GPU a dedicated 360), but since this would be a single pass 360 and your GPU model puts out a ridiculous amount of heat, it is probably a good idea. I'll also note that you could add a CPU to the front of the loop and wouldn't even notice it was added (as long as you were using a better pump).