The A/T servo on 777 is considerably lighter than that of 747 and 737, if you happen to rest your hand on it during idle operation, the servo can have a hard time erecting the lever back up.
The throttles on all Boeing North airplanes have the same force requirements to move - about 2.5 lbs force at the knob. In fact, with the exception of the 787, they all use minor variations on the same friction device for throttle 'feel'. Naturally, the 747 requires twice the force to move all the throttles since it has twice as many throttles to move. The autothrottle servo has plenty of force margin to move the throttles, its the friction devices that slip - as designed - to allow manual override of the A/T. The throttle quadrant on the 747-8 is unchanged from the 747-400.
That's roughly half the force that was required on the pre-FADEC throttle cabled engines - typically about 4.5 lbs at the knob (sometimes as high as 6 lbs.).
Boeing airplanes automatically select 'approach' idle when flaps are 25 or greater. By regulation, it must take less than 8 seconds to go from approach idle to 95% of max GA thrust (in actuality it's more like 5-6 seconds). I'm not a pilot, but I've been in the flight deck for a number of flight test go-around maneuvers (typically selected at 250 AGL) - 744, 748, 757, 767, and 777. I've never seen us lose more than 50 ft after TOGA was selected. The flight test airplanes are typically pretty light, but Asiana would have been fairly light since they'd burned most of the fuel on a 10 hr flight.