For a valid test, remember that the arm must be perpendicular to the load all the time.
Once the arm starts rising up, the lever decreases and the torque imposed to the servo by the very same load decreases as well.

I believe that the max torque happens close to the stall condition, for which the amps flowing throught the motor and electronic components is max (about 0.6 amps for standard servos).

IMO, a brief test cannot harm the servo, since it is just like a stall situation, which may happen anytime in regular use (due to excesive airspeed, linkage friction, wrong geometry, etc.)