This looks like a really good and big project. Those car-radiators are really bit tho, literally.

That L5640 is doing really good in 1.2v low-volt action. The chip seams to have more OC-headroom, but the BCLK-wall on MB seams to be limiting it.

Since you have 7 of them, it could be a good idea to see how they can do on a MB with higher BCLK-wall. BCLK240+ would make these chips rock @4.5GHz+, and it would be interesting to see if some MBs can do it.