160 kts & BuzzBox,
Our 767 Sim training indicates no controllability problems (1 wing tank empty/1 wing tank full) (confirming Boeing's view).
In fact, with the engine shut down as per the checklist, all the control inputs are generally neutral (due to the heavy wing compensating for the yaw! tank on the good side FULL).
Perhaps JSA, MFC, LER, JOC, or JME could shed light on this subject on behalf of Boeing ( or perhaps anonymously!!!)
GSV