Silverbird's info was correct before the changes, but all chests got easier with the changes. The level breaks still apply, they're just at different skill levels and I think level 5 & level 6 have different values now.
Someone needs to go to TC, get the skill check crystal ball from the Royal City, then go hunting in Ilshenar to get levels 1-6 chests, and start raising and lowering skills to see where the skill breaks happen.