John, you could move to an 8711 if you like but I don't think its necessary. The stabs on a yellow F-15 are fairly small so 8411's should be fine, not to mention the F-15 is hardly a speed demon. My Skymaster F-15 flew fine with similar servos on the stabs and it is ever so slightly larger. Once the plane is in the air there will be no buzzing as the airflow across the stab will neutralize the weight of the stab. I am sure I am using all the wrong terms and most likely David will point that all out but I prefer "simple" terms. Just imagine if you had something like an F-18 which has a ton of weight behind the pivot point of the stab, they make even 8711's buzz.