As for the 125 mm abrasive Systainer, I'm not a fan. It's too small for my liking. I made my own by tweaking Seth LS/RTS idea (link to talkFestool)
a little. Systainer #2 with 16 slots. I've got seven 125 mm sanding pads for my ETS/RO125 sander and ton of paper. I'd guess I could get nearly twice as many discs in there that I have shown in the picture, if I packed them tight.
As usual, nice job Brice. I've got the 6" systainer and don't mind the configuration for the sandpaper but you're set up offers a little more versatility. I don't have other pads that I need to store but if I pick some up I may reconfigure the systainer to accomodate them.