Your loop is made from quality stuff, its absolutely fine and should be cooling way better than a h100i.
I can only think that there is either little transfer from the CPU to the block or from the block to the radiator.
clean the thermal compound completely and and re-apply it either with the blob/line method or if your going to spread it, do it VERY thinly. If this is done properly, you can rule out its the transfer from your CPU to your block.
As for the block to water heat transfer, it can be to do with if the water block was screwed together wrong. I cant find the specific manual for your block but i have the supremacy one (which i own) and can use it an example.
http://www.ekwb.com/shop/EK-IM/EK-IM-3830046990563.pdf
If you ever opened up the block because you needed to change the socket mount plate or the Jet plate, you may have put it together wrong by perhaps screwing in the copper block so the copper fins are in the wrong direction.
From the link, go to step 3.1. to see what i mean. I know you have a different block but the concept is the same. You need to the copper fins to go horizontally if the Jet plate slit goes vertically. This is to ensure that water actually circulates the block. Also if your block might need specific Jet plate for your socket make sure you have the right one (it should have come with a variety of them if it does, if the supreme block doesn't come with extra Jet plates, then don't worry).
Lastly, i suggest you do a full rinse of your your system, you might have something blocking your loop.
Your waterblock is good enough, EK have replaced it with other ones but the difference you will see is literately a few degree's. I use the same 240mm radiator in my CPU + motherboard loop, and though i have a FX8350, i can tell you they run pretty hot at just shy of 5ghz. If i can keep that under 55 degree's (which is probably nearer to 70 realistically since AMD sensors are off), you should have no problem keeping your CPU down.
I also run a GTX 580 OC'd, but they don't come into the equation since they are not in your loop and run idle during prime95, so its definitely not the 580's that are keeping your temps high.
Getting another set of radiators wont fix the problem, it will just make it less noticeable, since what you have now is more than enough.
So this is what i suggest you do:
1. Clean your loop in case of blockages, Though you have a high flow block, your pump is the EK 2.2 and isnt the strongest. It usually is more than enough for just a CPU block, but if you have something gunking up the system you will see a performance drop.
2. Clean dust from Rad's
3. Check if your EK block is correctly set up ( copper fins perpendicular to the Jet plate slit)
4. CLEAN, then re-apply thermal compound but dont make it too thick (Gelid Extreme which a lot of EK blocks come with is electronically non conductive and is great)
After all this check your if your water in your loop is warm, and if you have not fixed the issue, you will at least be able to tell roughly where the problem is with this.
You have some of the best fans and decent radiators, no matter what your case is, air flow is not your issue. The GTX580's aren't your issue either because they shouldn't be producing any heat when your priming.
Changing stuff in your loop that doesn't need changing is not only expensive but inefficient, you have plenty of radiator to cool your clock, so the problem is actually before the rads, adding more will help a tiny bit but not enough to make it worth it or comforting. Same with the pump, it may be only a little pump, but as long as it has enough flow to keep the water temperature uniform, a better pump is only going to make more noise and no performance gain. If the pump isn't enough, its because something is blocking your system and once that is gone, your pump will be as good as any other considering your high flow loop.
