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The load is vertical IF this is a flush mount. If it is an articulated mount, the load is mostly torque attempting to pull the screw out of the stud. I would be very careful if this is the case.
A tilting mount is somewhere in between. Probably OK, but make sure the screws are in the stud solidly.
Let me know if the mount is articulated. This keeps coming up and really deserves a diagram.