I'm in 6b illinois. The trees I am growing with out problems are petes honey, hardy chicago, purple magnolia. The petes honey and hardy chicago no protection needed but likely you won't get brebas.
I have 3 desert king trees that were top killed. They will be protected this winter. Along with VdB, RdB, MvsB, black bethlehem, osborne proliffic, allbique pitete. And several unknowns. Those that I have more than one of I will leave one unprotected while protecting the other. Hope is that next season I will have some hard data as to cold hardiness, and protection.