Yeah, I went up on a personal training exercise with another pilot and did a number of things, including shutting down and feathering one engine, then both, checked out the glide speed and characteristics, deep stalled in power off and partial power settings in all flap and landing gear configurations, tried for VMCA......and also opened the door in flight to see how it handled. Apart from some added noise, as long as it was not being forced open into the airstream it made no difference at all. IIRC, the NZ PM (the female one that cancelled the RNZAF - Helen Clark?) was in an Aztec that had a door come open in flight as well. All in all, the Aztec would have to be the most forgiving and predictable light twin I ever flew.