On the heatsink question, I do have one concern on the center of the K64 or wherever two or more K64s share an edge (e.g. "K256"). That's centralizing a lot of heat in comparison. Just wanted to bring the topic up so that whatever heatsink selected/recommended they allow for a clear airflow path when they are placed side-by-side.
I think plain finned ones will be good for this, as you could have a fan on two of the end ones and a metal plate on the next so that air flows along in "lanes", either that or an up/down like some people are using on the asicminer blades.
I'm thinking gonna use copper or aluminum plating and flexible copper tubing to build water blocks. Passive water cooling will be WAAAY better than trying to worry about airflow, spacing, fans, etc, etc.