I've had instances be killed within a few minutes in peak hour. Would less busy zones with old processor architectures live longer on average?
The reasoning goes that they should be less busy and preemptible instances are designed to optimize dormant resources... of which old zones should have more of.
Update: While this question has an answer, it appears it would probably take a small collaboration ( or a medium to large business IT ) to answer this question... as such this may be better suited to a discussion board.