I don't know how to figure the Center of Gravity, but I always use 30% regardless of payload and it does just fine. One thing to take not of is that if I have full fuel tanks, I leave the trim at the setting it is at when the 767 first loads. If I have a 50% or less fuel, I put the trim setting at 3. That's the reading on the VC pedestal and not the Cockpit Tooltips info when you mouse over the Trim Wheel.

After takeoff and switching on the autopilot everything is fine....but before... oh,oh,oh......this is the time where my crew has to assuage the screaming and crying passengers, telling them......yes, we can make it..... we will reach safely our destination.
What is actually happening with the 767? I can't quite figure what you mean by that. :(

Mark