a club mate has this model fitted with an OS 81 FS and i must say its a beauty for 3D stuff. as for balance [c.o.g. ] i would set it up just slightly tail heavy for 3D flying . a good easy way to go from correct c.o.g to slightly tail c.o.g. is use a 6 volt pack firstly then go down to a 4.8 v pack for 3D , so set up the model right on the border line of c.o.g with the 5 cell pack first. as for servos any type with atleast 45 oz ins torque on 4.8 volts. if you can buy some [ INO -LAB servos grab them as they have heaps of torque / speed plus there coreless digitals and also cheaper than most Hitecs etc.