I've read just about everything I could find on-line, but it's just a fraction of what you've posted here.
In your researches, did you ever come across a handwriting sample for Mohamed Atta? (I've searched fairly extensively on the web, and I did find a sample for Marwan Alshehhi, but none for Atta.)
It would be of interest to compare any handwriting samples available with the handwriting in the anthrax letters.
But I seem to recall seeing something else...I will try to look.