Having spotted the new 40 slot trays from KaiserRushforth and needing a new box for my Anglian Spanish Civil War figures I ordered one with the new trays. Here are some pictures comparing the new tray to the existing 36 slot one.
First the two trays side by side (new one on the left):
Then close ups of the slots:
I've stuck with the 32mm deep trays and it's clear that unless you're storing spear armed figures or chaos spiky bits then the 40 slot trays are worth considering.