OK, we will put some of that comparison data together... probably over this coming weekend. We have tried a lot of experiments with outdoor supercomputing so we should be able to drum that data up.
We looked at the Variscite 4460 SOM a while back but we don't have any particular expertise with SODIMM. Are you only using that bus for power or is there a practical limitation to how many modules you can chain up that way?
As you probably know, Alex Ramirez (or just A-Ram in Barcelona) is espousing the Tegra board for his approach to hyperdense ARM servers. The Pandaboard is about .5U because of it's unique NIC arrangement, stacked over the USB, so you have to try out some exotic geometries to get better density. The MontBlanc board appears to be less than that... I guess these are the QSeven form factor? Check out from about 1:45 onwards at...