Thanks for confiming, Matt, I'm sure the OP appreciates it.
 
Well, my suggestion comes from a little of both.
The MCP655, is simply a very good, standard pump.
 
I'm cooling a pair of GTX590's and they really needed at least 4x120 worth of radiator space to be cooled properly. This is why I said a minimum--because obviously a quartet of 580's will output more heat.
 
I'm not an expert in water cooling, but you can (roughly) compute how large of a radiator by doing something like this:
1. Calculate the TDP of all the components you want to cool.
2. Multiply that number by 0.9 (electronics are roughly 10% efficient) this number is what you're aiming to dissipate in watts.
3. http://skinneelabs.com/2011-2012-radiator-comparison/3/ has a very nice comparison of Fan RPM to Watts dissipated at set flow rate. Use that chart in determining exactly how much "rad" you need.
 
I'll do some of the legwork myself:
The TDP of a single GTX 580 is roughly 250W. 
You have four, but when accounting for efficiency, you get 900W.
Looking at that chart I linked, each 3x120 rad is capable of dissipating roughly 450W @ (1500RPM/1.6GPM)
As you can see, my earlier suggestion of 2x(3x120) is pretty close.
 
But, the moment you mentioned nodes in a cluster, I realize you are not the typical SR-2 customer...you sound like you have experience in complex server setups. Not to mention, this isn't going to be a workstation where someone will have to listen to the fans blowing full bore. So if we take that into account, then according to the same chart, you could potentially get away with a single 3x120 rad for all 4 GPU's, but you would need 4000RPM fans.
 
I hope that takes the guesswork out of things. 
 
EDIT:
I seemed to have neglected the concept of delta. Well, I could make my post even more absurdly long, but it's easier just to provide the linkage: 
http://www.overclockers.com/guide-deltat-water-cooling/

As for the cooling, I like the MCP655, one of the best out there, if not THE best pump.  For connecting the cards on your loop, you have several options.  You could just cut a piece of tubing and run that between cards, or go with this type of fitting (has worked great for me):
 

 
For radiators, I tend to go for MORE than I probably need, but my temps stay VERY low, even when folding.  With 3 x 590's (if on same loop as CPU) I would go with at least 2 x 120.3 rads.