The gearbox doesn't have to work as hard if you get a good balance between the barrel and the mechanism. The spring helps. You can also flatten the stop tabs so the mechanism arm spins 360 degrees. Only problem is that internally, the gearbox has a lot of slop, so when the arm travels past the apex, it suddenly drops a bit.

Another problem I've found is that some Tamiya worm gears have barely visible casting imperfections that make the motor more noisy when running in one direction than the other. I replaced a Tamiya motor with a Heng Long one (drop-in replacement) and the noise disappeared. Who woulda thunk it?

I think that gutted servos would probably give better performance since they have a higher quality construction and tighter tolerances (but would be more work/fun to fit. I've just been too lazy to experiment.)