RE: micro servo
I've used the Futaba 3101 and the Hitec HS85 both with nylon gears and with complete success. But i would'nt use the Futaba 3114 The gear train is just to fragile for me. As far as the HS81 i did use it once the pot wore out to quick for me. The HS85 has better electronics inside along with a better gearset than the HS81 just to explain the cost difference.
You will not need a metal geared servo for your throttle not on your application.