Loop load advice ?

The pump needs are based on the blocks in the loop for the most part, not the heat generated. Have you already purchased some of the equipment or are you still planning the layout? It would be very helpful if you gave an itemized list of loop components. The question isn't whether a single rx360 can handle your components, but how well it can handle them. A 680 and 3570k would do fine on a rx360 rad, but you probably wouldn't have much overclocking headroom.

Do you plan to use this machine for gaming or other less CPU-intensive tasks? For a gaming rig, I think you would be best off with cooling your video cards first, with a nice air cooler on the CPU. Then if you have space/budget, add the CPU to the loop.

AC blocks are nice, not really low restriction but not really high either. Personally the 360 is fine, especially for a single GPU and a CPU. I ran a single 360 with my 275s SLI and 2600k and temps were around 60C full load on both GPUs and the CPU. Personally, I would stick to a 360 get a D5 the GPU and CPU block and since I HATE GPU fans I would also get a block for the second GPU. Also you would have plenty of room to overclock on a RX360 with the 680 and 3570K, and you would honestly be fine with 2 680s on there with it as long as you had good fans and did push pull like I did. It was still a heck of a lot quieter than a single radial fan let alone two.

Stock a 275 TDP is 219 Watts, I had two highly overclocked so much more likely 250w each plus the 2600k at 4.8Ghz on a single 360. A 680s TDP is 195w so should not be a problem at all, also it looks like [H] did a lightning review and in their setup the OC vs stock lightning drew 12 (or less in most of the tests they ran) more watts. A 275 OCed would pull about ~30w more each.
Edited by DarkHollow - 11/11/12 at 2:37pm

That should be fine for sure for single loop and only a few blocks. The only thing I have to say against it is some of the reliability problems I have seen on OCN. Other than some occasional issues with the pumps dying prematurely they seem to be a good cheap pump.

I'm not overly experienced with SLI, but I've never heard that one card performs less computations than the master. The temperature of the master card is typically higher because the slave card blocks the airflow. Is this what happened in your last build or was the master actually working harder? I'm confused why you want to overclock your CPU, but not your 2nd video card. For most games, a 3570k at stock is satisfactory. With a decent air cooler, you could get a pretty good OC. Water cooling will allow you to edge out more overclock if your chip is capable. The gaming performance difference between an air cooled OC and a water cooled OC will be very small, if there even is one.

For the most part, there is little hope that you won't want to upgrade your loop eventually. Water cooling is a (functional) hobby, it's too much fun to tweak things.

Personally, I would go with a more powerful pump unless you are set on not upgrading. My personal choice was the mcp 35x, but it's relatively costly.

To save some money, I would go with a universal gpu block. You'll need to put heatsinks on your VRM modules with this option. The advantage is that all you need is a ~5$ mounting bracket if you buy a new card, saving you the cost of a new waterblock.

What fans do you have/plan to buy? RPMs matter, but static pressure is the important characteristic for a radiator fan.

I was confused with the cooling needs of a 680. One 360 rad should be fine for a single gpu and CPU, but probably would struggle if you ever decided to add your 2nd card.

Edit: For CPU air coolers, I have always had a personal bias towards Zalman. Here's one on newegg - http://www.newegg.com/Product/Product.aspx?Item=N82E16835118046
Edited by tulanthoar - 11/11/12 at 3:55pm

The difference between OCs may be minimal but would you call a loaded temp of ~75c vs ~55c trivial? I would much prefer to have my CPU nice and cool in addition to overclocked, not to say 75c isn't safe but when your putting so much into the cooling system anyways why not cool the cpu? Not like you need a new block every cpu.

I have to agree however with this

The EX360 likely wouldn't be enough for all 3, the rule is typically 120mm of THICK rad space per component and your good. A RX360 would be fine with all 3.

I do have to say that a universal block mean you have to make sure you still have good airflow over the vrm and ram sinks. Also the cooler the vrms the less power they use and the higher you can OC (usually, but every card is different). Of course its not the only factor but its one and it makes a difference. Unless I am mistaken SLI of 2 different clocked cards lowers the faster one to the slower speed. Therefore to OC, both would need to be, but again this may be different on 680s what with the boost and all. My 480s both got plenty hot and the one on water could OC quite a bit farther than the air one in addition to using less amps on the VRMs at load and idle.
Edited by DarkHollow - 11/11/12 at 4:27pm

Hmm when did they do that? AFAIK it was always downclocked to the slowest cards speed.

Looks like that's about half right on 680s. According to a guys testing on EVGA forums:

Edited by DarkHollow - 11/11/12 at 5:05pm