I do both of those, but I maximize STR and INT so I can carry more loot and cast more spells. But even with a skeleton key (does it raise my GM Lockpicking to 110?), I get the hissing gas.
Im looking for a idea of how much higher DEX will help. All of the resources I can find say higher DEX helps lockpicking, but I was looking for a more precise answer. For instance, if I raise Dex fro 10 to 30, my chance of opening a L6 treasure chance increases fro xx% to yy%.