Alot of that is sound reasoning based upon hints, Rasler. All of it seems accurate with the exception of you placing the Privaron Espada at the bottom. This is untrue as many Privaron Espada have shown more resistance than any Lieutenant could stomache and much more.
Also with Tosen and Ichimaru we are completely in the dark. I can't help but notice you leaving out Urahara. You do him a massive disservice as he is the creator of one of the plot lynchpins which is basically a device to unlock untold power. That of inofitself should hint at his power. Not to mention that he is quite capable (and he proves this) of toying with a Espada. Not to mention that it is still very much doubted that he is a regular Shinigami, if one at all. I can't help but think that all you fans who are grossly underestimating Urahara will be in for a very big shock.
It also seems to me that all of the truly powerful Shinigami don't tend to stay with the SS. They are always banished, defect and or not members.
There's my two cents.
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