I'm thinking of water cooling some quad socket boards, each of which hold four quad core Opteron 8346HEs (79W TDP).

The water block I am most likely be using is the OCZ HF-MK1, but the XSPC Delta V3 may be a possibility.

Pump will either be a Laing D5 or Phobya DC12-400/EK DCP 4.0, both of which I have spare.

Would you think it better to run a single loop, or one per board?

It would be nice to run both systems through a single radiator, but this may not be very practical as the total power load is 632W.

I've been looking at the 4x180mm radiators, but I'm not sure if it's be a more sensible investment to buy two 4x120mm radiators, or a 9x120mm, for example.

Thank you for your time.