EDIT: I have heatsinks on back of all boards in regulator area, and 120 CFM fans!
Does the backside of the regulator even get hot? I have felt the top of the chip and its very hot but I don't feel much on the backside. Wouldn't putting a small heatsink on the chip do more?
For the hashing chips those thermal vias work well as even touching the vias themselves gets hot, even better with a heatsink.
Yes, it gets quite hot. I believe they are also constructed do dissipate the heat to the board, but I did not do any research in that matter.
In my opinion the regulator heatsink is much more important than chip heatsinks.
+1, the most important task before serious overvolting of the h-boards (0.8V+) is to first stick heatsinks on the back side of the board under the regulator. If possible, stick a heatsink on top of the regulator and the inductor. This way you can take them as high as 1V. The board will dissipate close to 70Watts at 1V.