I posted about it here (
Legendary Mapmaker's Glasses (skill stacking) ) but basically it seems like the stacking of Carto above GM isn't working at the moment. I'd be interested to see the impacts of 101-105 cartography on chest quality (rusty/metal/gold).
Apologies as these are kind of partial results because I wasn't tracking all details when I started jotting down how many gold chests but what I've found so far is that when I've dug up stash or supply with 100 carto & 2500 luck they have all been gold chests. I've dug up 5 cache maps (I think 3 at 3500 and 2 at 2500) and I got 4 gold chests and 1 metal chest. I've dug up 3 hoard chests (all 2500 luck) and I got 1 gold chest (very first chest I dug up after release), 1 metal chest, and surprisingly 1 rusty chest.
It looks like there is some kind of calculation done that definitely takes your Carto into consideration when digging different levels of chests (maybe luck does too). That being said, based on the language of it
it doesn't seem like chest quality will absolutely impact loot. As many others have said before, I've gotten lots of junk in just about every gold chests I've dug up so far and by comparison that 1 rusty chest I dug up wasn't far off from the items I've had in gold or metal chests.