How many 28mm figures do those mantic cases hold as I can't see any dimensions on them.
I'v managed to fit 20 corporation marines in a small case, and you could fit double so in a large one.
For small vehicles and big cavalry/support weapons, the large cases should be perfect for 2 or 3 units.
I have seen a few pictures of each case holding 15 gw marines with room for the odd character.