personally, for that size plane, I feel that a standard, nylon geared servo is just fine. I doubt you plan on ripping the thing around like a 3D plane so My personal choice for a Warbird of that size would be my go-to servo the Hitec 311. I used to buy them by the truckload so I have lots laying around new-in-box. Other guys would recommend Futaba or maybe JR or Spektrum servos. My dad has used the Tower Hobbies brand servos and Hobbico servos in his similarly sized planes with plenty adequate results. Good luck with the assembly!