[gbanger]

There are way to may variables to even think about a simple answer to that one George.
A lot of manufacturers supply stall torques. But the load on your servos changes every second you are in the air and where you have the sticks and exactly what you are asking the aircraft to do at the time.
I have not done enough reading on the subject to give you the answer you are looking for, but the problem could be high resistance in a solder joint or a connection between the reciever and the servo.
I know its a pain but try swaping the servos to different connections on the reciever. If the problem stays in the same servo then bin it. If it goes away it could be a connection at the reciever.
If another servo works OK on that reciever output then once again its probably the servo.
If the servo is doing it with no load (sitting on the ground) then bin it.
If you really want to get technical you can do a load test on the servo and see if there is a problem.
I have never had a servo twick that didnt have an internal problem, when they do that mate you bin them. Not worth loosing a plane over.
Remember these things only draw milliamps.
I run a stand alone BEC on my big Sukhoi 140 and the battery for that is only 2S 1000mah and that is running 5 x 18 kg servos, it comes down after a 6 minute flight at nearly 4 volts per cell.
I am building a Seagull Super Tucano at the moment and will be running 8 x high torque 12 kg servos through a Dualsky 80 amp ESC and the BEC in that supplies 5.5 volts at 5 amps.
I dont think it will be a problem................Fingers crossed.
Its good to remember to engineer your aircraft so they are reliable and safe, but dont over do it and add weight that dosent really need to be there.
Test it before you fly it!