Attached Link: http://www.morphography.uk.vu/public/unitbox.zip

I had thought of exploring this further with the community's help. The 3D modelling forum is probably the best place to do it, but since we're discussing this anyway, I may as well kick off here.

The attached link is a simple cube in OBJ format, 1 unit per side. If you have a modeller which can read real-world units, import the file without scaling and see what size it appears to be.