The large drawer isn't much smaller than a sys1 - have you looked into the possibility of trimming the C12 insert down slightly, so it fits in the drawer? I think I saw on here somewhere that someone had done it with the PS300 insert. Might be worth looking at (if you haven't already).

I stack a systainer 2  on top of a sortainer 4.  the Sys2 has all my drilling accessories (hole saw kit, 2 driver bit sets, etc) and my battery charger.  My sort4 has the makita 18v drill & impact drivers in the drawer, with a small assortment of screws and anchors in the small drawers.  The medium drawer holds my drill index, some spade (paddle bits) and a few other loose items.  Sorry I have no pics to post, but its late.

I also have few other sortainers (a total of 10 ) with various consumable items I use at work.  I carry everything in, stack it up (systainer still on top) and everything is accessible.  I really like this setup.