Hey there,
we have started a Wiki post with some basic information here: The Official Wicked Wiki
You can find tables there with basic information on different equipment tiers. Unfortunately we did not fill it with more data yet (so far). But your post gave me the idea to maybe get some upgrade data there as well, like another table with basic values of upgraded equipment.
Maybe we’ll wait out the next update and see what maybe changed. And maybe some more people from the community and/or the dev team will help with filling the wiki.
Otherwise you might just have to experiment a bit. But i think equipment tiers 1<2<3 … and material can be a starting point. I am sure fully upgraded plate will def. be better than fully upped leather for example, but also requires other upgrade materials. Since we have to wait for the update anyways, why not upgrade a few pieces and see where the values go?