Jason,
In my experience, the "standard" tube produced by tube suppliers is 2mm wall thickness. Deviation from that is "possible;" the tube suppliers can make your tubes to whatever spec you need. Personally, I stick very close to this 2mm standard at a minimum; my "thinnest" tube I use is 1.75mm thick. I will not go any thinner than that, as my opinion is that you would be trading off durability, for only minimal weight reduction. Meanwhile, other tubes I use are spec'd as thick as 2.6mm. It's based on design requirements, etc. -- but this is the way I do things, for whatever that is worth. I THINK this is what you are asking...
If you have other, specific questions, send me a PM and I'll glad to try and help as best I can!
Thanks,
Steve