Safety, what is more important?

[Klem]

Is there a formula or rule of thumb for the increase or decrease in velocity/pressure from bullet seating depth?
For example a load with a 120 grain bullet that generates 2500 fps seated at 2.200 OAL, what will it be if seated at 2.290 ? (bullet in not touching lands in both cases).

This is the essence of what an internal ballistics program like Quickload does. If you can get the algorithm out of them I will be surprised.